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/testdata/testapply_2/deduplicate_by_--selector/log

@@ -0,0 +1,65 @@
+processing file "helmfile.yaml" in directory "."
+first-pass rendering starting for "helmfile.yaml.part.0": inherited=&{default map[] map[]}, overrode=<nil>
+first-pass uses: &{default map[] map[]}
+first-pass rendering output of "helmfile.yaml.part.0":
+ 0: 
+ 1: releases:
+ 2: - name: foo
+ 3:   chart: incubator/raw
+ 4:   namespace: default
+ 5:   labels:
+ 6:     app: test
+ 7:     component: raw
+ 8:     index: '1'
+ 9: 
+10: - name: foo
+11:   chart: incubator/raw
+12:   namespace: default
+13:   labels:
+14:     app: test
+15:     component: raw
+16:     index: '2'
+17: 
+
+first-pass produced: &{default map[] map[]}
+first-pass rendering result of "helmfile.yaml.part.0": {default map[] map[]}
+vals:
+map[]
+defaultVals:[]
+second-pass rendering result of "helmfile.yaml.part.0":
+ 0: 
+ 1: releases:
+ 2: - name: foo
+ 3:   chart: incubator/raw
+ 4:   namespace: default
+ 5:   labels:
+ 6:     app: test
+ 7:     component: raw
+ 8:     index: '1'
+ 9: 
+10: - name: foo
+11:   chart: incubator/raw
+12:   namespace: default
+13:   labels:
+14:     app: test
+15:     component: raw
+16:     index: '2'
+17: 
+
+merged environment: &{default map[] map[]}
+1 release(s) matching index=1 found in helmfile.yaml
+
+Affected releases are:
+  foo (incubator/raw) UPDATED
+
+processing 1 groups of releases in this order:
+GROUP RELEASES
+1     default/default/foo
+
+processing releases in group 1/1: default/default/foo
+getting deployed release version failed:unexpected list key: {^foo$ --kube-contextdefault--deleting--deployed--failed--pending}
+
+UPDATED RELEASES:
+NAME   CHART           VERSION
+foo    incubator/raw          
+