MAF file validation

[jakevc]

After fining out that we were submitting incorrect MAF formatted variants for the ERBB2 and EGFR insertions, I realized it would be easy to catch this in validation with some simple rules about the ref and alt allele that would force the correct MAF format for insertions as well as deletions:

https://docs.gdc.cancer.gov/Data/File_Formats/MAF_Format/

Pseudo Code for test:
ValidateInsertion: If mutation.is_insertion: require(Reference_Allele=='-')
ValidateDeletion: If mutation.is_deletion: require(Tumor_Seq_Allele2="-")

[thomasyu888]

Thanks @jakevc . We are tracking this internally on Jira: https://sagebionetworks.jira.com/browse/GEN-582. But will leave this open to update you.