Enhancement : Use Event End times

[bbdoc]

Now that we have event start/end times in our DB, wouldn't it be a good idea to take it into account while scanning for Pokemons ?

When an event ends, all pokemons of this event will automatically disappear. If we could add the pokemon_id to the event table (through Madmin), we could easily set the end time of those pokemons scanned during the event duration to the max between the event end time and the actual end time. This way, once the events end, all pokemons disappear from our maps automatically and we don't end up with a map full of pokemons that are not there anymore.

It would also be good in terms of webhook so the webhook receiver would automatically announce the end time of the event as the disappear time of the pokemon.