Fix WindowContext leak

The root causes of this issue are:
  1. WindowTokenClient#attachContext makes WindowTokenClient has strong
     reference to WindowContext, which leads to WindowContext cannot be
     GC'd.
  2. WMS#removeWindowToken needs MANAGE_APP_TOKEN permission which
     normal apps don't hold.

This CL does following things:
  1. Use weak reference instead on WindowTokenClient#mContext.
  2. Relax WMS#removeWindowToken to check callingUid if
     MANAGE_WINDOW_TOKEN permission is not held
  3. Deliver config changes to the client side in
     WMS#addWindowTokenWithOption
  4. Some minor fixes

fixes: 150812449
Bug: 150715095
Test: atest WindowContextTest
Test: atest WindowManagerServiceTests
Test: atest WindowTokenTests
Test: atest WindowManagerPermissionTests#testMANAGE_APP_TOKENS
Test: atest
WindowManagerPermissionTests#testADD_WINDOW_TOKEN_WITH_OPTIONS

Change-Id: I9f1d73af2abb78fc9844e6d9eb25e9f0293514e7