Improve filters: fix SuspiciousOperation in regex filters

This is the same as #256 just moved it to a branch on the this repo.

>If the path is prefixed with MEDIA_URL it will be replaced with MEDIA_ROOT (updated in 1b0ba0d)

>Related to #251
It will be better to name the regexp groups instead of using positional arguments, is more easy to read and understand the code for future devs.