no real changes but replace manual calls to Set{Text,Bk}Color() with matching calls...

no real changes but replace manual calls to Set{Text,Bk}Color() with matching calls to restore original colours with constructions of local wxTextColoursChanger objects which do this automatically; also renamed the old wxColourChanger class to wxBrushAttrsSetter to make it more clear what it does and reduce the risk of confusion with the new class

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53151 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775