Fix assessing is current value for eu suspensions downloads and speciesplus

- Updates the Admin interface to properly display if an eu suspension is current
- Makes sure that EuSuspensions are marked as current for SpeciesPlus, based on their start and end events
- Makes sure that for EuSuspensions the start date displayed is the one from the event
- Makes sure that the SpeciesPlus download of current eu_suspensions uses the start and end event to calculate the value of is_current