For Travis CI - only install what being requested.
Route system exit request to Exit menu handler to perform exit check.
Instead of storing Geometry pointers, store shared array pointers for triangle mesh collision data. This protects against the original Geometry resizing its data.
Enhanced focusable button to be drawned differently when focused.

Also:
- Revert back base Button class to non-focusable as it turns out it has negative side effect (e.g toolbar button becomes "sticky"). Create new focusable button style instead.
- Prevent double Alt+F4 from terminating Editor with unsaved changes, bypassing warning message box. System exit request is in fact ignored when there is any modal window waiting for user input.
Merge remote-tracking branch 'remotes/grking/master'
Refactored check for dynamic buffers into a function.
Added PhysicsWorld::RemoveCachedGeometry() function to manually invalidate cached collision geometry of a changed model. Added watching for CollisionShape model live reload. Removed internal but public functions from the Lua physics API.
Merge branch 'master' of https://github.com/urho3d/Urho3D
Restored previous Geometry::GetRawData() function (though it leads to duplicated code) to prevent unnecessary copying of shared array pointers.
Travis CI: API documentation update at 2014-01-03 08:53:13 UTC.
[ci skip]
Improved the "Overall structure" documentation page.