Implement the visual display of MOC data in Firefly

Initially, display the HEALPixels actually identified in the MOC (which is just a list of HEALPixel IDs in NUNIQ format) as polygons overlaid on a sky display in Firefly. Include this in the usual Firefly layer control behavior.

• We would like multiple MOCs to be able to be displayed at once, with selectable colors used.
• It may be useful to enable the control of both polygon boundary colors, transparency, etc. as well as polygon fill with adjustable transparency.
• Be able to switch between outline (wireframe) and transparent color fill
• MOC show as a HiPS layer with checkbox off, should lazy load with any HiPS

Implementation technical Notes:

• We should read the table using our normal fits table reading and put all the rows (only one column) into the store.
• Each number (NUNIQ) can be translated to a HealPix level and number and then to 4 WorldPt corners using functions in HipsUtil and HealpixIndex
• We need to make new DrawObject will need to be created that can draw a filled polygon, fill with a transparent color for overlaying. Possibly we could modify FootprintObj or MarkerFootprintObj. 
• If the points reduce to a single point (based on zoom level) it should draw a single point.
• The drawing layer should be able to change the color in our standard way.