Updates for the Ginga remote control plugin

	modified:   ginga/Control.py
	modified:   ginga/FitsImage.py
	modified:   ginga/PythonImage.py
	modified:   ginga/misc/plugins/RC.py
	modified:   scripts/ginga
	modified:   scripts/grc.py

- updated the Ginga remote control plugin to be more general
  - now can call almost any method on the Ginga shell or any channel object
Added grc to installed scripts

	renamed:    scripts/grc.py -> scripts/grc
	modified:   setup.py

- changed name from grc.py to grc
- added to installed scripts in setup.py