Make WindowState use config from WindowContainer

Previously WindowState updated its config only when it was either
requested to relayout the window or to report resize to client.

This CL makes WindowState to use WindowContainer's configuration
handling model. Configuration can be updated any time by parent
window container or any other caller. Also we're saving last
reported to client config to be able to check if there is something
new since last report.

Test: Manual and existing tests still pass.
Change-Id: I832acdb950871b85b7c16becde16d58de392faf5