MS-RDPEGFX Initial Implementation (WIP)

Initial implementation of MS-RDPEGFX in xfreerdp.

* Parsing of all egfx pdus
* RDP8 bulk decompression
* Define callback interface for all messages
* Implement egfx surface management
* Implement egfx bitmap cache
* Decode uncompressed, RemoteFX and planar codecs
* Start ClearCodec decompressor (incomplete)
* Fix and improve parts of virtual channel system

There are still some graphical artifacts and ClearCodec is not yet supported. The /gfx option can be used to enable MS-RDPEGFX in xfreerdp. When ClearCodec is received, a pink rectangle is drawn instead to show parts that are not supported yet.