Bugfixes for start/stop (route-based) entities + db update

Fixes for start/stop

• calendar_dates sourced departures: in certain cases the feed does not provide consistent information on trips that start today but in reality are tomorrow
• offset was not properly applied
  addresses: #166 and #164

Fix for automated source/feed update:

• if the url to update the data failed, the existing database was already deleted, laving the user with 'nothing'. This is now improved, addresses: #168