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
diff --git a/packages/SystemUI/shared/Android.bp b/packages/SystemUI/shared/Android.bp
index 710b5f7..defc49b 100644
--- a/packages/SystemUI/shared/Android.bp
+++ b/packages/SystemUI/shared/Android.bp
@@ -20,6 +20,10 @@
         "src/**/I*.aidl",
     ],
 
+    static_libs: [
+        "SystemUIPluginLib"
+    ],
+
     // Enforce that the library is build agains java 7 so that there are
     // no compatibility issues with launcher
     java_version: "1.7",