Change the exposure-lib to use the `AbstractDatabase` class for database polymorphy
The exposure-lib currently is derived from SpatiaLiteDatabase. To be able to provide an abstract layer for the user/programmer, it must be based on the AbstractDatabase class so that it can be connected either locally to a SpatiaLite database or to a server-based PostGIS database. This change is necessary so that we can develop the distributor and builder such that these programs can be used for local exposure data creation as well as for the server-based model.
This change may result in a fundamental change of the exposure-lib but should leave the interface the same.