Change branch structure to that of Opencast

[KatrinIhler]

AS discussed in the Dev meeting and similar to opencast/opencast-admin-interface#229, we should adopt the branch structure of the main repository (so develop and version branches) so we can get bug fixes into the legacy releases without being blocked by breaking changes.

[mtneug]

How would releases be tagged?

[KatrinIhler]

Good question. Right now it's just the date, right? So I guess a combination of date and OC version would do?

[mtneug]

Why include the date if we already have a major version? We could go to the typical number system, i.e.

{opencastMajorVersion}.{editorReleaseVersion}

So basically matching major versions of editor and Opencast are compatible. Or is this confusing?

[KatrinIhler]

IMO we can only do this if the version numbers line up with those from Opencast, otherwise that could be confusing.