fixed osx config/data dir being in the wrong place, closes #459.

Added migration module to contain any of those fixes that have to be performed
before startup.
fixed missing cls argument #459
fixed problems with migration on OSX #459
Use the same MIME types for serving files as are used for transcoding.
Merge pull request #466 from cheese83/devel

Use the same MIME types for serving files as are used for transcoding.