Add plugin API for individual QS tiles

This will allow prototyping of individual QS tiles and/or their
visual representation without having to write a plugin for the
entire panel. This will allow quick iteration on QS UI + dual
target tiles.

Test: Install plugin using new API
Change-Id: I05ca9d9f5a200a1dad2c3582251a36edb5cb9aba
40 files changed