[MS-RDPEGFX] ClearCodec, H264, YCbCr

ClearCodec: complete implementation
RDP8.1 H264: WIP implementation using OpenH264
YCbCr: integrate HP's YCbCr converter for planar codec
Memory alignment: make libfreerdp-gdi buffers memory aligned

New command-line arguments have been added: /gfx-thin-client, /gfx-small-cache, /gfx-progressive, /gfx-h264. With this pull request, the basic RDP8 graphics pipeline codec profile is completed (RDP7.1 RemoteFX, Planar, Uncompressed and ClearCodec). The progressive codec is not supported.

* leaked memory on realloc fail 
* and realloc(NULL, sz) == malloc(sz)