[WIP] Refactor FilterUtil to Doctrine 2

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #118
| Refs tickets  | #1205
| License       | MIT
| Doc PR        | 

TODO:
- [ ] Fix Category Filter Plugin #1205
- [ ] Update Docs and move them to the Main docs Folder.