[Feature Request] Add logging methods to who ends/deletes giveaways

[AverageFemale]

Our server allows members to host their own giveaways, so we also allow them to end/delete their own giveaways (until now of course). Recently some of our giveaways have ended up being ended early with no explanation of who, if anyone, ended it or if the bot is glitching and ending it prematurely. This would be a useful feature to have for servers that allow members to create giveaways of their own but wanna allow them to /gend their giveaways as well.

[jagrosh]

I think this and #227 can both be addressed simultaneously for ending giveaways manually by adding a new line to the final embed, or modifying the default "Ended" line.

As for deleting giveaways, I don't have a good solution off the top of my head, so I'll need to put more thought into it. Once a giveaway ends or is deleted, it and its entries are completely removed from GiveawayBot's database. Logging giveaway-related activity to a channel or webhook seems like a feasible option, but the setup for that could end up confusing for most users.

[AverageFemale]

Would it be possible to just do a simple:
/logchannel channel:#loggers
And then have the bot create a webhook and store the url in the database?