1. Sorry for the size, but this PR was all-in or nothing
2. The mechanics for namespace is that user selects it via the dropdown
   and the selection goes through all pages, but has effect on display
   only on list pages.
3. The selector is now ugly. I'll style and improve wording later.

This includes a huge refactor to extract pod list common code from RC
deatails to a separate directory. With this, though, it can be reused in
lots of places (e.g., in Daemon Sets).