Database connections are not re-established if they are lost of some reason

[Zharktas]

Describe the bug
If databases connections are lost for some reason, like restarting database server, the connections are lost and datapusher+ produces an error. The logs show the following:

sqlalchemy.exc.OperationalError: (psycopg2.errors.AdminShutdown) terminating connection due to administrator command
SSL connection has been closed unexpectedly
[SQL: INSERT INTO apscheduler_jobs (id, next_run_time, job_state) VALUES (%(id)s, %(next_run_time)s, %(job_state)s)

To Reproduce
Steps to reproduce the behavior:

1. Restart your database
2. Try to add CSV to datastore via datapusher+.

Expected behavior
The data would be added to the datastore

[jqnatividad]

Thanks for the report @Zharktas .

Now that DP+ uses PostgreSQL instead of sqlite for the job history, will need to make the DB connection more robust.

[jqnatividad]

This will be fixed when we release DP+ 1.x, where we convert DP+ to a CKAN extension, so we won't need to use apscheduler anymore.

cc @tino097 @TomeCirun