Let apps developers edit version notes, expose it in the API (bug 945858)

- Let developers edit release notes for hosted apps
- Store release notes in ES on the app
- Add id field to version API results to make it more useful, enable CORS
- Add release notes to app and app search API results
Change wording from 'Version Notes' to 'Release notes' (bug 945858)
Merge pull request #1492 from diox/releases-notes-for-hosted-apps

Let apps developers edit version notes, expose it in the API (bug 945858)