Orphan gender filter

Jira story: https://osraav.atlassian.net/browse/OSRA-204

- Added gender filter to Orphan index view similar to the one we have for Sponsors
- DRYed gender string constants and put them in yaml config file
- DRYed custom filter feature

OSRA-204#Code-Review
I can revert back to %w[Male Female] and address this later, or we can leave it here this time and add a chore to fix all settings later. I don't mind either way.