Fix UTC conversion in GTFS

* UTC offset was in minutes, departure-times in seconds
* UTC offset should have been subtracted
Correct GTFS parser tests

West of the UK/Ireland, UTC is higher than local
Fix GTFS parser test 2/2

Correct same mistake as in the parser, UTC offset is in minutes
Merge pull request #506 from bliksemlabs/fix_gtfs_utc

Fix UTC conversion in GTFS