Various stuff

-Removed some data members from top level SerializerBase interface to
eliminate indirection of using virtual inheritance
-Removed virtual inheritance from MongoReplicableSerializer, removed
MongoReplicableBase entirely as its functionality only matters when
serializing
-MongoReplicableSerializer::generateUpdateQuery() now returns a two-stage query when items are removed from an array, due to the way mongo handles removing array items.
-Added a baseline to replicable - when initially serializing it will
create an initial baseline, which can be used to communicate initial
state with other processes or with the database. This baseline does not
update with future serializations.