adding a document/text file that describes by design plan (WIP)
REFACTOR: split slon_dbconnect() into two so parts can be reused for
logical replication connections
WIP - remote WAL listener
base support for launching a WAL listener instead of a normal remote listener
adding .SQL files for PG 9.4 with logical replication extensions

We make the sl_table and sl_sequence time travelled tables
extract the list of tables to replicate from sl_table

We now also determine the tables origin by joining sl_table with
sl_set we depend on sl_table being time-travelled for this