Filter prefixes

[hrshdhgd]

• Added a new function filter_prefixes: This filters the msdf.df to contain only those mappings with prefixes that are present in a list provided by the user.
• Add class method remove_mappings() to MSDF class. Addresses one checkbox in Lexical mapping analysis and feedback/review monarch-initiative/mondo-ingest#49

[matentzn]

I approve this, but if you really want to make me happy you can add a CLI method

remove(msdf1, msdf2)
  msdf1.remove_mappings(msdf2)
  write(msdf1)

[hrshdhgd]

Your wish is my command!

sssom remove abcd.sssom.tsv --remove-map def.sssom.tsv -o abde.sssom.tsv` 

should work.

[matentzn]

Excellent, left a few comments but nothing that blocks merging. THANKS

[matentzn]

This is great, we can later consider making this multivalued (not now). Thank you!

[matentzn]

this is new, I assume there was no test for the else case?

[hrshdhgd]

This was missing and became apparent when only 1 value to a param was given for e.g. --subject_id ABCD:1234 instead of multiple --subject_id ABCD:1234 --subject_id DEFG:4567. The missing ) that's added in the code above threw an error. There was no test to check this.