[Mac] fix link label breakage after e7586f3e35c1250116015a14547eccd18e3d1fd4
[Mac] Fix combo boxes after e7586f3e35c1250116015a14547eccd18e3d1fd4
[Mac] fix color chooser sample
major refactor of stock commands to be more like existing monodevelop command system
[Mac] fix crash when tree view SelectedRows count is zero
add CommandStatusRequstHanderAttribute and Mac backend implementation
get rid of unused command stuff