Merge branch 'ingar/png_icons' into 'master'

Ingar/png icons

Replaces BMP icon images with PNG images, this allows for better icon transparency.

See merge request !8

diff --cc radiant/gtkdlgs.cpp
Simple merge

diff --cc radiant/mainframe.cpp
Simple merge

diff --cc radiant/patchmanip.cpp
Simple merge

diff --cc radiant/texwindow.cpp
Simple merge