Overlay: Add Direct3D 11 support

* Based on an initial patch by Benjamin Jemlich
* Effects11 code based on changes by nyet

Cleaned up, direct3d 11 related changes only from the previous pull request #177.


This PR adds **overlay support for Direct3D 11**.
This has been verified in Crysis 2 (main menu), Saints Row 3, Civilization 5 (Demo).
Additionally, as verified with a self compiled SimpleSample.exe from the DirectX SDK using Direct3D 9 - the direct3d 9 **overlay now displays in more cases** as well.

It adds the **fx11 (Effects 11) library** as a submodule dependency.
A qmake project file has been added to allow compilation of it as a dependency. On building the mumble_ol.dll (overlay) it is added as a static library, thus no additional dll is necessary.

A build has been *tested* to not break stuff on Windows 7 x64 (pre-SP) with
* Crysis 2 (11)
* Blacklight: Retribution (11)
* D3D examples (SimpleSample.exe for 9, 10, 11)
* Smite
* Guild Wars 1
* Guild Wars 2
* Dota 2
* Awesomenauts
* Wolfenstein: Enemy Territory (OpenGL)
* Team Fortress 2 (menu)
* Battlefield: Bad Company 2
* League of Legends (menu)

I did not review nyetwurks d3d11 state block and drawing code (yet).
But it works.