Make public JournalSettings

[umbreak]

Migrating from 0.100 to 1.0.0 we noticed that CassandraPluginConfig was changed in favour of JournalSettings. We were using CassandraPluginConfig to create/reuse a CassandraSession with the same configuration as the cassandra plugin. Also to reuse keyspace and other configuration flags (autocreate, for instance).

If JournalSettings would be public, we could keep doing it the same way. For now, I had to copy paste some code from that class.

How we were doing it using 0.100: https://github.com/BlueBrain/nexus/blob/ab784387d68a8fccba1da1806b5c2369cfb957cb/sourcing/projections/src/main/scala/ch/epfl/bluebrain/nexus/sourcing/projections/Projections.scala#L82

How we had to do it using 1.0.0: https://github.com/BlueBrain/nexus/blob/1.4.0_iam_refactored/sourcing/projections/src/main/scala/ch/epfl/bluebrain/nexus/sourcing/projections/Projections.scala#L82

Thanks

[patriknw]

From 1.0.0 we wanted to minimize the public api surface.

Note that the CassandraSession can be shared via the CassandraSessionRegistry.