Filtering: vcf_filter.py: added possibility to include a path to custom filters python file, not only a local script file

[gitanoqevaporelmundoentero]

vcf_filter.py: local-script argument changed to custom-filters, since now it is possible to include a path to custom filters python file

[sambrightman]

@martijnvermaat I think this also needs closing in its current state: needs rebasing, no tests, some typos (usage, function name) many unrelated changes in the commit.

The core idea is fine if it's cleaned up and rebased. I'm not sure if it's the "right" way to allow plugins, but if it works and someone wants it then it seems okay. Probably should maintain backwards compatibility with existing method?

[martijnvermaat]

Yes, should have closed this before. As @sambrightman says, the idea may be ok, but not in this form.