project configuration inheritance

[faryon93]

It should be possible to inherit settings from any other project.
Values that should not be inherited:

• name
• hash

In addition a special project type, called "meta project" should be introduced, which is not ment to be processed by a build pipeline. It is simply a storage for common configuration values. The meta project should not appear in the web ui in the leftern navigation bar.

With this modification the config file should be much cleaner and repetitivly configuration is avoided.