Move plugin support to shared lib

In addition to changing imports, this required some changes to use java
7, since that's what the shared lib needs to be for launcher.

See bug for more details on this project.

Test: "atest com.android.systemui.shared.plugins"
  build succeeds and all tests pass

Bug: 115877296
Change-Id: Ib79ede0a61664df0ba1a194632a345d2229777fc
30 files changed