Changes the ImplicitGeomeryHolder class to accept Visitors on itself
instead of deferring the call to the prototype geometry. This fixes the
occurence of some CCM errors during checking and is required for the
implementation of the planned topological checks.

fix solid self intersection incorrectly ignoring degenerated triangles depending on planarity settings

Adds the handling and creation of the embedded database in RAM, which is
used for the in-memory and fallback modes.

Adds the CppTest marker-interface to exclude Healer tests that  were
interfacing with CGAL from the build. These tests are needed for the
development of the replacement library, but shall not cause build
failures in the meantime.

Removes the AUTO_SERVER=TRUE flag for H2, which was used for debugging
and causes a Firewall popup in the compiled binaries due to opening a
port for local access to the embedded database. Denying the Firewall
request has no impact on CityDoctor, as its connection uses the
embedded mode of H2. Accepting the request does not allow remote access
to the database, as by default H2 rejects any connection from remote
machines.