• fixing TaskBase.__call__ so submitter is not overwritten
• improving checksum_states so it doesn't calculate the content hash of big files for multiple times (using files_hash that keeps track of all the files)
• removing output after task is run to save memory
• adding Directory, int, float, bool, str, and list to the types allowed by output_spec of ShelloCommandTask.
• adding python 3.9 to GA
• fixing GA singularity workflow