Add tillerNamespace and kubeContext to helmDefaults. Also add merging of args capability.
People can start adding additional fields under helmDefaults on top of this. The additional fields are merged to args as long as they are implemented using the framework introduced by this commit.
Changelog:
* adding merging for helm defaults args and --args, adding tillernamspace, kubecontext to helmdefaults, adding getargs to lint command
* adding docs for helmdefaults
* checking if empty default values
rmartinez3