Replace embeds in queue channel on startup

[mattwells19]

Description

To align with the vision of "as few messages as possible," the queue channel needs to get reset whenever Norm restarts. That means deleting all current messages and then sending the version embed, the current queue embed, and any active matches.

We'll want to create a new text channel for this so that we don't lose any conversations in our current test-queue channel. It'll make it easier for deleting all of the messages as well.

Acceptance Criteria

On start, the following takes place:

• All messages are removed from the queue channel
• The version embed is sent (this is handled as part of Send Embed with current version  #5)
• The current queue embed is sent (already implemented)
• An active match embed is sent for each currently active match
• The leaderboard channel is updated with the latest stats for the current season (already implemented)

Just to be clear, only the items in bold are in scope for this ticket. Everything else mentioned should just be taken into consideration while doing this work.

[mattwells19]

What if we took this opportunity to redo how we get channels and send messages in those channels. Like a DiscordChannels class that takes the NormClient as a parameter in the constructor and allows you to access the channels. Maybe it can keep track of queue messages internally as well.