GUI "Seven-fication" & compressed data changes

Some user interface elements have been changed to a more Vista/7-like
look, mainly by changing the fonts used, and by adding a TaskDialog to
serve as the GameDataManager's error message box during data loading, if
when supported by the OS; added static wrapper function ShowErrorMessage
for this in GUIHelpers, also removed the old GetSuggestedGUIFont
function previously used by the editor controls; removed support for
compressed files from BaseFile class, as any compressed set of game data
is decompressed on detection anyway; also added decompression of the
game's two main fonts and removed support for compressed fonts from
FontRenderer; probably some other, minor changes/fixes...