added uuids filtering + argument

[IsslamElkasah]

I created this branch because I needed to transfer only specific submissions from one project to another.

• I added a new optional argument --filter-uuids to specify the location of a txt file with a list of uuids to be transferred.
• Edited the main()
• Edited get_src_submissions_xml() to accept the filter file (if provided) and added the necessary code for filtering and removing submissions which was not provided as uuids in the txt file. If the file was not provided, the code works as before and will transfer all submissions from src to dest.

[joshuaberetta]

@IsslamElkasah sorry for the delay in responding here. I like the idea but this can be implemented better now with the work I did in #17 to transfer submissions based on UUID values. Do you want to rework your PR to support this? Otherwise I'll close this PR and create an issue to do it another time.