Merging mast-names into Master

This branch rewrites the pipeline's filename handling, in order to adopt the requested MAST conventions. The development process for this branch, as well as the new convention, is documented in Ticket #143.

The major changes to the code are as follows:
* filenames now require metadata from the input image header.
* a new function that will attempt to convert the targname entry in the image header to a name known by JPL ephemeris. If no match is found, the targname is used, to a maximum of 20 characters.\
* The output filename dictionary is used more than ever in determining the names of the actual output files. Most importantly, there is now a dependence on the order of names within the lists of the output dictionary. See [here](https://github.com/STScI-Citizen-Science/MTPipeline/issues/143#issuecomment-51701003) for more details.