Refactor VepInterpreter.pm and add a new vep annotation filter

Refer to AT-628. For ACMG report, a new vep filter is needed to remove all variants that hit neither splice sites nor non-synonymous coding sites.
should we add a "valid_values" list here?  I guess ideally it would be auto-generated, but I don't think that is possible - we would have to manually maintain the list when we added a new category.  I am up in the air about whether it is worth it or not.