Tool GUI library evaluation

This infrastructure proposal evaluates our options in terms of GUI libraries we could use for tools that will be part of the asset pipeline.

Requirements for the GUI library

 * Qt-based
 * Python bindings
 * Support for Qt Designer & Python code generation
 * Available on Win32, Linux, Mac
 * Free of charge
 * Compatible with GPL 3.0

Contenders

 * Pyside
 * Pyqt