Add support of list of exclusion in settings.py

[makaleks]

First, thank you for this nice package!
I have some directories and files in media/ accessed from django-filebrowser (file cloud in admin). My shell gives me command history, so I always add as many --exclude arguments as I need. But my project will be used by other people, who can miss some files and some logic will be broken. I believe a good solution is to have a list in settings.py containing strings - elements of --exclude.

[akolpakov]

Good idea