Add !archive message command

[JJRcop]

This command takes up to two messages and archives any messages between them

If provided with one message it archives that one

Uses PartialMessage instead of Message for argument conversion, so you can archive deleted messages if you still have the link. This also means that without a full message link including Channel ID the command may archive incorrect messages from the current channel.

Notices have been set up to inform about this.

What does this PR add/fix/improve/...
You can now archive specific messages or a range of messages.

Migration
No migration required however some translations need to be created for a couple of new tokens

Dependencies
None

[JJRcop]

Feedback welcome on using PartialMessages. I did it for speed so the bot doesn't need to fetch the messages before getting on with the archiving, however this does mean since they are partials they are not verified to be in the right channel if a channel ID is not included.

This is safe, the worst case is some messages posted around the same time from the current channel are archived instead, as that's what the PartialMessage converter does.

A side-effect is you can use links to deleted messages and archive those.

I could make a custom converter extending PartialMessageConverter to reject arguments without channel IDs.

[JJRcop]

I could make a custom converter extending PartialMessageConverter to reject arguments without channel IDs.

I've done this here: 3162fc4

But I don't want to add it to the PR just yet because I am happy the way it is now, just made that to expand the available options.