D3D: Add exclusive fullscreen support.

This PR adds support for exclusive fullscreen when "Render to Main Window" is disabled. Please test it out and provide me with some feedback so I can polish things were necessary.

Build available at: https://dl.dolphin-emu.org/prs/pr-506-dolphin-latest-x64.7z

### To-do
- [ ] Restore original window size when switching back from fullscreen.
- [x] Set fullscreen upon initialization of the backend if it is enabled.
- [x] Restore exclusive fullscreen when focus is returned after Alt+Tab.
- [x] Fix deadlock when stopping emulation in fullscreen. (PR #515)

### Considerations
Will exclusive fullscreen be an option or always on? Would such an option will be the default or optional?

At this moment I consider support for OpenGL or "Render to Main Window" outside of the scope of this PR, unless such support is considered essential before adding this feature.

### Fixed issues

Issue [6713](https://code.google.com/p/dolphin-emu/issues/detail?id=6713) and [7334](https://code.google.com/p/dolphin-emu/issues/detail?id=7334) should be fixed by this change.

3D vision support is restored in DX11 with a much cleaner implementation which fixes issues [3979](https://code.google.com/p/dolphin-emu/issues/detail?id=3979), [4726](https://code.google.com/p/dolphin-emu/issues/detail?id=4726), [4732](https://code.google.com/p/dolphin-emu/issues/detail?id=4732) and [5990](https://code.google.com/p/dolphin-emu/issues/detail?id=5990).

It may also help Nvidia Optimus detect Dolphin as an application that requires high performance, can anyone test that?
I suggest moving the second condition into a nested if. Feels like the better thing to do when a short condition follows a very long one, as in this case, because it makes it easier to understand this code quickly.