RdTk, PNG read/write, Shadow X11, RDP8.1 Display Control

RdTk (Remote Desktop Toolkit):
* Start lightweight in-memory widget toolkit
* Add basic bitmap font rendering with alpha blending
* Add Label, TextField and Button widgets
* Add android nine patch rendering (scalable images)

libwinpr-utils:
* Add lightweight png read/write support (lodepng)
* Add support for reading images from memory rather than files

Shadow X11:
* Fix extended keys
* Add PAM-based authentication

RDP8.1 Display Control:
* Update edisp virtual channel
* Fix egfx dynamic resizing in libfreerdp-gdi
* Add resize notification on egfx resize