Add override and merged config to WindowContainer

This consolidates usages of override and full (merged)
configs in WM objects and also adds support of per-display
configurations. Having full configs allows us to get
current applied config at any level.

Test: Manual tests pass. Added some new to WindowContainerTests.
Change-Id: I996770433c80da41265f3e14048bd23cead097f9
12 files changed