Improve schema.deegree.org handling and hosting

[stephanr]

The current http://schemas.deegree.org website is filled from a build job running after a release.

This currently has two disadvantages, since there is no history/backup of the schema files and the update is outside the git universe in a shell process.

In order to make this process more trackable, the following approaches could bring an improvement here:

• Manage all schemas.deegree.org within a github repository (for History and Backup purpose)
• Switch the publishing process to download schema changes and publish these to the github repository
• Furthermore, the hosting could then be moved to the github (pages) CDN