Introduced new window management.

Introduced new window management.

Continuation of patch proposed by Marcin Łapiński.

[Issue]    https://bugs.tizen.org/jira/browse/TT-157
[Problem]  There was no proper views management
[Cause]    N/A
[Solution] New class ViewManager for controling switching
           between views.
[Verify]   Launch browser > switch between different
           views (page view, more menu, settings, etc.),
           check if switching is correct check if there
           are no relevant warnings in logs.

Change-Id: I8827964b6539ecb7a4c02edd3d296b72a149a9e7
Signed-off-by: Maciej Skrzypkowski <m.skrzypkows@samsung.com>