Persist data for 7 days after the bot is kicked from the server

[acollierr17]

Right now, the bot immediately deletes all data relevant to the server after it's removed. I'd like to persist this data for 7 days. If the bot isn't re-invited in that grace period, then proceed to delete the data. However, if the bot is re-invited, cancel the timer.

[acollierr17]

Will be building a microservice to handle the bulk of this operation.

[acollierr17]

Here is the microservice being built at https://github.com/suggestionsbot/guild-expirations