Wait for database availability (fixes database errors when created from QuickStarts or --from-code)

Minor fixes and also an action hook that will force a wait for the PostgreSQL availability. 

Tiny Tiny RSS creates all database tables on startup, however for that to work we must wait until the database is up and running before starting the application.

This will make --from-code and also the QuickStart work properly:

https://www.openshift.com/quickstarts/tiny-tiny-rss