Reconfigure Cassandra dblog tests

This commit makes the Cassandra-backed LogTest subclasses run serially
and also permits messages with DEBUG or higher severity in both the
console and target/test.log output.  The goal of these two changes is
to make difficult-to-reproduce LogTest failures slightly easier to
analyze using the log alone.
Unify names of IDAuthority impls/tests

We used a mix of manager, authority, and allocator to refer to what
was fundamentally the same type, which survives this commit unchanged
as "IDAuthority".

This commit does not touch "IDManager", which is distinct from
IDAuthority.  Nor does it touch VertexIDAssigner.  Just IDAuthority
implementations and tests.
Renamed TransactionHandle to BaseTransaction

Also renamed TransactionHandleConfig to BaseTransactionConfig, renamed
the builder, several methods that refer to the type, and a javadoc
comment linking to a method with an affected type in its signature
Removing references to gollum-site