Refactor VepInterpreter.pm and add SpliceNonsynonymousFilter.pm

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.
We could make this a more generic "category" filter and allow the plan to specify which categories should pass.  I'm not sure if other categories will be needed in the future or not.