Add RARFileSource as internal filter.

Allows RAR files without compression to be played without unpacking. Code from: http://www.v12pwr.com/RARFileSource/

Things that *might* need to be changed:
* Move RARFileSource to the thirdparty directory, since it's not our code.
* Disable compiling RARFileSource as standalone filter, since it's not our filter.
* Convert spaces to tabs and other styling issues. (not our code?)
* File.h in the original code conflicted with unrar, thus I have renamed the classes in there. (better solution?)
* Remove the ReadMe? And what about the License?