Add SunPy colormaps to ginga-sunpy.
Merge branch 'master' into rajul
Add sunpy colormap finding and commit database changes.

This does two things:

* create a sunpy map on file open to compute the colormap name
* adds a 'Commit changes to Database' button to commit the database to file.
*
Small performance optimisation in creating SunPy map.

Only create the map when opening a database file from the metadata
in the AstroImage instance, this is to save SunPy having to open the
fits file etc.
Merge pull request #1 from Cadair/rajul

Some bonus stuff!