Add NOT NULL and UNIQUE contraints on tables

[lonvia]

This adds NOT NULL and UNIQUE constraints to SQL tables consistently were possible. These constraints may allow PostgreSQL to optimise execution and helps catching subtle errors in the SQL code. The PR includes some fixes for these kinds of errors:

• importance wasn't set where our secondary importance raster has holes
• array_merge() would sometimes return null, leaving name or address vector null
• search_name no longer contains any entries with an empty name vector
• suspicious country areas are now ignored in the location_area tables

The PR also makes sure that indexed_status is only set to 1 when a place is newly added. This allows to skip deleting data from secondary tables for new data, shaving off about 5% of the import time.

Finally fixes an issue in the BDD test with the randomly generated names sometimes not being valid and improves termination when an error occurs during indexing.