Add support for one model handling multiple media types

like an Image model
Support content with '/' in the id
Re-added load from master
Merge pull request #69 from Connexions/multiple-mediatypes

Add support for one model handling multiple media types
Merge remote-tracking branch 'upstream/master' into regressions
Merge pull request #68 from Connexions/paths-in-ids

Support content with '/' in the id
Merge remote-tracking branch 'upstream/master' into regressions