Allow passing dictionaries instead of names to ActivateAddons

reasons:
- allow completing vundle emulation {rtp keys}
- allow version locking, eg user can do
   call ActivateAddons([{name: "foo", tag: "bar"}])
- If vim-pi switches format so that each repository can contain multiple sources
  users can pass 'source-from': "github" or "vim" like hints per package.
  (future story)

Nicer vundle like api could be introduced such as VAMActivateWithOptions
command (arg and options)