add new interfaces for classes using database access and configuration

The reason for the more generic is that the old IMcmUser interface was locked to
the MongoConnectionManager which may not always be the case.

A further interface should be created later that specifies how a connection object
should be implemented.

Also added an extended interface for MongoDB specifically.
Merge branch 'T324'

* T324:
  add new interfaces for classes using database access and configuration