[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.

don't we leak memory with this early exit that doesn't cleanup ?