This PR removes the need to run setup_timescaledb. It also fixes
pg_dump and pg_restore. Previously, the database would restore in
a broken state because trigger functions were never attached to
meta tables (since setup_timescaledb() was not run). However, attaching
those triggers at extension creation also causes problems since the data
copy happens after extension creation but we don't want triggers fired
on the data restored (that could cause duplicate rows, for example).
The solution to this chicken-and-egg problem in this PR is to have
a special configuration (GUC) variable `timescaledb.restoring` that,
if 'on', would prevent the extension from attaching triggers at
extension creation. Then, after restoration, you'd call
restore_timescaledb() to attach the triggers and unset the GUC above.
This procedure is documented in the README as part of this PR.
If a user attempts to setup a database while not connecting using
the network, port is NULL and thus fails constraint checks. Instead,
we now use the default Postgres port of 5432 when this happens.
Also, setup_db() is renamed to setup_timescaledb() for clarity in
the presence of other extensions.
