Fix broken selector and DAG calculation logic after --{include,skip}-needs addition with correct Release IDs (#1823)

#1772 broke `--selector` with `needs` in many ways.

The two biggest problems I've encountered were:

- duplicate releases even if you've provided a proper `selector` to deduplicate
- sync/deletion ordering broken when you have `needs`

For the first issue, we had to update `getSelectedReleases` function to also calculate the "selected releases and releases needed by the selected releases", and use that to calculate the DAG. That should have been done in #1772.

The latter started happening after I've fixed the first issue. The source of the issue was that `needs` turned out to be ambiguous in a few cases.

Previously, `needs: ["foo/bar"]` had two meanings. One for "needs release bar in kubecontext foo", another for "needs release bar in namespace foo".

Moreover, `needs: ["foo/bar/baz"]` had three meanings.

- `needs release baz in tiller namespace foo and namespace baz`
- `needs release baz in namespace bar in kubecontext foo`
- `needs release baz in tiller namespace bar in kubecontext foo`.

Especially, the first meaning doesn't make sense at all. Helm 2 solely use tillerNamespace for namespacing the release and Helm 3 uses namespace for that.

This fix sorts all the bugs and issues I've found so far around that, by changing the meanings of the above two examples as follows:

- `foo/bar` means `namespace=foo,name=bar` for Helm 3 and `tillerNamespace=foo,name=bar` for Helm 2
  - `needs release bar in kubecontext foo` is now `foo//bar`. Notice the extra `/` between `foo` and `bar`.
- `foo/bar/baz` means `kubecontext=foo,namespace=bar,name=baz` for Helm 3 and `kubecontext=foo,tillerNamespace=bar,name=baz` in Helm 2

Fixes #1818

pkg/app/destroy_test.go

@@ -442,25 +442,25 @@ merged environment: &{default map[] map[]}
 
 processing 5 groups of releases in this order:
 GROUP RELEASES
-1     default/frontend-v3, default/frontend-v2, default/frontend-v1
-2     default/backend-v2, default/backend-v1
-3     default/anotherbackend
-4     default/servicemesh, default/database
-5     default/front-proxy, default/logging
+1     default//frontend-v3, default//frontend-v2, default//frontend-v1
+2     default//backend-v2, default//backend-v1
+3     default//anotherbackend
+4     default//servicemesh, default//database
+5     default//front-proxy, default//logging
 
-processing releases in group 1/5: default/frontend-v3, default/frontend-v2, default/frontend-v1
+processing releases in group 1/5: default//frontend-v3, default//frontend-v2, default//frontend-v1
 release "frontend-v3" processed
 release "frontend-v2" processed
 release "frontend-v1" processed
-processing releases in group 2/5: default/backend-v2, default/backend-v1
+processing releases in group 2/5: default//backend-v2, default//backend-v1
 release "backend-v2" processed
 release "backend-v1" processed
-processing releases in group 3/5: default/anotherbackend
+processing releases in group 3/5: default//anotherbackend
 release "anotherbackend" processed
-processing releases in group 4/5: default/servicemesh, default/database
+processing releases in group 4/5: default//servicemesh, default//database
 release "servicemesh" processed
 release "database" processed
-processing releases in group 5/5: default/front-proxy, default/logging
+processing releases in group 5/5: default//front-proxy, default//logging
 release "front-proxy" processed
 release "logging" processed
 
@@ -648,9 +648,9 @@ merged environment: &{default map[] map[]}
 
 processing 1 groups of releases in this order:
 GROUP RELEASES
-1     default/logging
+1     default//logging
 
-processing releases in group 1/1: default/logging
+processing releases in group 1/1: default//logging
 release "logging" processed
 
 DELETED RELEASES:
@@ -713,12 +713,12 @@ merged environment: &{default map[] map[]}
 
 processing 2 groups of releases in this order:
 GROUP RELEASES
-1     default/frontend-v1
-2     default/backend-v1
+1     default//frontend-v1
+2     default//backend-v1
 
-processing releases in group 1/2: default/frontend-v1
+processing releases in group 1/2: default//frontend-v1
 release "frontend-v1" processed
-processing releases in group 2/2: default/backend-v1
+processing releases in group 2/2: default//backend-v1
 release "backend-v1" processed
 
 DELETED RELEASES:
@@ -783,12 +783,12 @@ merged environment: &{default map[] map[]}
 
 processing 2 groups of releases in this order:
 GROUP RELEASES
-1     default/frontend-v1
-2     default/backend-v1
+1     default//frontend-v1
+2     default//backend-v1
 
-processing releases in group 1/2: default/frontend-v1
+processing releases in group 1/2: default//frontend-v1
 release "frontend-v1" processed
-processing releases in group 2/2: default/backend-v1
+processing releases in group 2/2: default//backend-v1
 release "backend-v1" processed
 
 DELETED RELEASES: