first experimental use of pyvo to query source catalogs
added SIA-accessed image server support
tried adding configuration settings that set the location of the server files; doesn't quite work
Merge branch 'master' of https://github.com/RayPlante/ginga into rayplante-catalogs
Some edits to merge with current usage of Catalogs at Subaru

	modified:   ginga/Catalog.py
	modified:   ginga/Control.py
	new file:   ginga/VOCatalog.py
	modified:   ginga/gtkw/plugins/Catalogs.py
	modified:   ginga/misc/plugins/CatalogsBase.py
	modified:   ginga/qtw/plugins/Catalogs.py

- created new catalog type VOCatalog, which absorbs most of Raymond Plante's
  changes to Qt Catalogs plugin to use the pyvo module
- parameters to the different services can now be given an order so that
  they always show up in the ideal order in the GUI
Remove added data directory

	deleted:    data/catalogs
	deleted:    data/image_archives
	deleted:    data/plugin_Catalogs