New library 'qt'

This new library (in branch yake2) provides a few useful niceties which can prove to be helpful when creating applications with Qt.

It provides a few generic multi-edit widgets (combobox, lineedit, checkbox…) with a common interface based on value-string validators (and boost::any). So as long as you provide the value-to/from-string and equality operator functions you can work directly with the represented values (e.g. int or struct) instead of doing the conversion from/to-strings manually.

This library is still work-in-progress - the basic techniques have been tested & proven before in a different context (and code base).

The property browser/editor for (game) classes and objects uses this library - resulting in leaner code which is also easier to understand, imho.