Gtfs: change validity pattern split

since calendar.txt is not a mandatory file (calendars can be filled by
calendar_dates.txt too) we need to do the validity pattern split after
having read both file.
Gtfs: limit production period to one year

we can handle more than one year in navitia, so we limit the production
period too
Gtfs: change a log
Gtfs: add test for missing calendar dataset
Merge pull request #503 from antoine-de/fix_calendar_split

Fix calendar split