Revert "framework: fix reference leak in activiy manager"

This reverts commit a723c67bb5f95a4d039f96c2bcb62e44b01d1af5.
Revert "[WIP] Multi-window"

This reverts commit cada625b129d8fca243c85bda848c79c7402230a.
Revert "ActivityTrigger:  New class to invoke when activity starts/resumes"

This reverts commit da90bdbc4e06a958225bab1ac7d28c445348c5bb.