Integrate Clear the Queue stats into a Bubbles command

[TimJentzsch]

We previously had a separate script to generate the stats for CtQ.
However, we have better options now with the upgraded API and should make it more accessible by putting it into a Bubbles command.

The command should be !ctqstats <start_date> <end_date>, where <start_date> is the start of the event and <end_date> is the end of the event. The end date should be optional and default to start date + 12 hours.

The old script is available in this repo, but it's rather outdated in some parts so we can probably only reuse the graph generation.