Fix cx_Freeze build and add LogikSim.ico.

cx_Freeze did not detect all required modules. Added
explicit include of PySide.QtXml. Changed output
exe name to LogikSim.exe.
Added application icon and preliminary about dialog.

* Added resources.qrc file which compiles to resources_rc.py
and is used for the MainWindow UI icon.
* Added an "About" and an "About Qt box"
* Extended setup.py to package LICENSE and AUTHORS file
* Modified setup.py to generate windowed exe

Known issues:
* Icon resolution is to small. Ideally we need an svg version
  of the icon to use for everything besides the .exe icon.
* When starting the .exe you can still see a console window
  pop up briefly. Probably not cx_Freezes fault as this also
  happens if you rename main.py to .pyw and launch it. No
  idea what causes this.