Invoke "remove" middleware on DELETE requests

Instead of removing documents with a direct MongoDB query (Model.remove()), first retrieve them from DB and then call the remove method on those documents instances.
Merge pull request #90 from lukaszfiszer/invoke-remove-middleware

Invoke "remove" middleware on DELETE requests
Merge remote-tracking branch 'origin' into development
Fix an issue where remove middleware wasn't called.  Special thanks to lukaszfiszer\!