[X11] GetEntryAssembly may be null.

When running under NUnit GetEntryAssembly returns null. In this case we instead
search through the AppDomain for an assembly that matches the AppDomain name.
Merge pull request #194 from Frassle/getentryassembly

[X11] GetEntryAssembly may be null.
Add To/From sRGB methods to Color4.
Add To/From HSL methods to Color4.
Add To/From HSV methods to Color4.
Add To/From XYZ methods to Color4.
Add To/From YUV methods to Color4.
Add To/From HCY methods to Color4.
Merge pull request #197 from Frassle/color

Colorspace conversion functions.