This is done by moving app.Context to internal/mobileinit,
introducing mobileinit.SetCurrentContext and,
making bind/java depend on it.
TODO: check gomobile bind's proguard rule - context lookup
was implemented through reflection on android.app.AppGlobals class.
Change-Id: Ieb6ad503eeef8c2c1c5836a21c667938c5a701a2
Reviewed-on: https://go-review.googlesource.com/12279
Reviewed-by: David Crawshaw <crawshaw@golang.org>