Automatic merge from submit-queue (batch tested with PRs 41621, 41946, 41941, 41250, 41729)

Refactor printers and describers into their own package.

This sets the stage for using printer code from the server side (decoupled from kubectl) and loosens the coupling between kubectl and the printers. `pkg/printers` contains interfaces and has an import restriction against pulling in API specific code, while `pkg/printers/internalversion` can be used for internal types.

Add a method on `Factory` for retrieving PrinterForCommand which uses the Scheme and RESTMapper from the Factory, not the hardcoded ones.  This further separates kubectl from the core API scheme and allows better composition.

Change NamePrinter to use RESTMapper (previously it was hardcoding those conversions). This means that we now return plural resource names (`pods/foo`) but is correct once aliases and shortnames start being returned by the mapper.

This is a prerequisite for server side get, but is pure refactor (contains no new features).

@deads2k @liggitt