Further work on Pica emulation

Pica/Math: Improved the design of the Vec2/Vec3/Vec4 classes and simplified rasterizer code accordingly.

- Swizzlers now return const objects so that things like "first_vec4.xyz() = some_vec3" now will fail to compile (ideally we should support some vector holding references to make this actually work).
- The methods "InsertBeforeX/Y/Z" and "Append" have been replaced by more versions of MakeVec, which now also supports building new vectors from vectors.
- Vector library now follows C++ type promotion rules (hence, the result of Vec2<u8> with another Vec2<u8> is now a Vec2<int>).

Pica/citra-qt: Replace command list view and command list debugging code with something more sophisticated.

Fix threading for Qt5.

Note: There is a pre-existing issue with booting a new game in that it keeps the old EmuThread.
The GL code now supports this but the Core still doesn't.

Connect the emu_thread start/finish to a moveContext slot.

Remove documentation for external modules.

We don't need these and they clutter up the repository.

Added FS functions to Archive and Archive_RomFS

Removed unused citra.h

Common: Add a clamp function to math_utils.h

ARM: Remove a forgotten const in vfp.

Revert "Removed redundant loop in EmuThread::run()"

Use Qt5 by default for citra-qt project.

Core: Use std::array for managing kernel object space

Common: Get rid of an unnecessary forward declaration in symbols.h