Removed png folder from tests. For Ticket #152.
Removed the creation of a separate png folder within the project folder. For Ticket #154.
Removed png folder from make_output_file_dict. For Ticket #152.
Merge pull request #155 from STScI-Citizen-Science/no_png_folder

Accepting this merge removes the separate png output folder, to comply with MAST conventions. For Ticket #152.