Creating ds9 region overlays

[ktfhale]

We should be able to use the information we use to draw PNG overlay so create ds9 .reg files which will plot similar overlays atop FITS images when they're opened in ds9. The format is simple, just a list of commands:

image;circle(500,500,3.0") # color=blue text={blah}

Will draw a circle at the pixel 500,500 with a radius of 3 units (I don't think that's inches) using the image's coordinate system, and will label it 'blah'.

I figure it's best to use the image coordinate system. We could use RA and DEC, but I figure it's best to maintain uniformity with the png overlays.

[ktfhale]

I've added a function to generate these region files, but it's currently untested. I'll need to actually have a mysql database with at least one png file before I can really test it.