[Enhanced Monitoring] Show Approximate Progress of Initializing Phase

[vjeeva]

During the initializing phase of pglogical, we don't see ANY progress on how much data is being moved, how much is left, etc.

The only things we can see are table sizes and database sizes, as well as pglogical.show_subscription_table(), which can show replication status per table (however only during replication, during initializing the status of a table is unknown).

To the status command, show the following:

• Per datacenter, show a column of <Dest DB size>/<Src DB Size> to show progress, and another column for a percentage based on that
• Per database, show the above column. Also, show another table of per-table statuses as follows: column of /, column for percentage, and another column for status (whatever is shown by pglogical.show_subscription_table() for status and unknown == initializing).

See #176 on details about pglogical.show_subscription_table().