Support for namespaced tiller

[foobarto]

With RBAC and in a scenario where single Kubernetes cluster is intended to be used by multiple teams it's very useful to have tiller deployed in separate namespaces (one per team for example).

With helm CLI this is done by installing tiller in specific namespace like this helm init --tiller-namespace=ateam or by specifying env var TILLER_NAMESPACE=ateam.

Kubernetic right now doesn't work with tiller deployed in other than default namespace.

[jmccann]

We have some namespaces with it's own tiller. So would be nice to allow even not just specifying a different singular namespace for all contexts but a different tiller namespace per context.