4.1.0 (2018-11-26)

calendar_dates: properly store calendar_dates as schedule_exceptions. (d819f33)
editor: allow null values for foreign ref fields allowed to be empty (d63d0fb), closes catalogueglobal/datatools-ui#224
editor: permit empty values if required field allows it (40ef82d), closes catalogueglobal/datatools-ui/#237
export: make sure TimeFields are always exported in proper format (a3a1721)
exporter: ensure GTFS feeds with only calendar_dates are exported properly (40fd8d6)
fields: round outputted double feeds to avoid excessive precision (2a770b2)
snapshot: check for null namespace in tableExists method (5b87be8)

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