Misc fixes to run under Python 3

	modified:   ginga/AutoCuts.py
	modified:   ginga/Catalog.py
	modified:   ginga/Control.py
	modified:   ginga/PythonImage.py
	modified:   ginga/RGBMap.py
	modified:   ginga/cmap.py
	modified:   ginga/gtkw/FitsImageGtk.py
	modified:   ginga/gtkw/plugins/Info.py
	modified:   ginga/gtkw/plugins/PixTable.py
	modified:   ginga/gtkw/plugins/Thumbs.py
	modified:   ginga/imap.py
	modified:   ginga/iqcalc.py
	modified:   ginga/misc/Datasrc.py
	modified:   ginga/misc/Settings.py
	modified:   ginga/qtw/FitsImageQt.py
	modified:   ginga/qtw/QtHelp.py
	modified:   ginga/qtw/plugins/Catalogs.py
	modified:   ginga/qtw/plugins/Contents.py
	modified:   ginga/qtw/plugins/FBrowser.py
	modified:   ginga/qtw/plugins/Info.py
	modified:   ginga/qtw/plugins/PixTable.py
	modified:   ginga/qtw/plugins/Thumbs.py

- fixes to various plugins and modules to run correctly under python 3