[FEATURE] export aabefore and aaafter in peptideindexer

Add aabefore/after and start/end in protein to hits generated by PeptideIndexer.
Note that or formats so far only export this information for the first peptide evidence so this can be seen as a preparation for mzidentml/mztab support.
jep.
You can additionally compute this in the outer loop. but that's probably overkill.