WL#3663: Plug-in interface for slave replication module

# SITUATION

Currently, the replication part of the code that applies database changes on the
slave side is an integral part of the server code

# PROBLEM

It is not possible to create and distribute special-purpose solutions in a
practical manner. In addition, it is impossible for third-party developers to
create their own solutions.

# SOLUTION

Make the slave part of the replication code a dynamically loadable module with a
well-defined interface towards the server code.