Discord: Split messages if necessary

[BenWiederhake]

Old behavior: Telegram user sends a huge 4096-byte message (the maximum permitted by Telegram), it gets clipped to 1950 bytes on Discord.

New havior: Set MessageSplitMaxCount=3 as config option of the Bridge, and it instead sends up to three messages to Discord (each of maximum length)

Note that this handles editing correctly, both in the "bot user" and "webhooks" cases.

This PR combines well with #2123.

I have no write permissions to the wiki, so I cannot add the appropriate documentation there.

[BenWiederhake]

Changes since last push: Refactored Bdiscord.webhookSend as suggested by the codeclimate bot.

[codeclimate]

Code Climate has analyzed commit a91a14c and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	1

View more on Code Climate.

[42wim]

@BenWiederhake thanks for looking into this and adding tests 👍
The wiki has set readonly because of spammers. I've invited you to the matterbridge/wiki on https://github.com/matterbridge/wiki/wiki if you want you can updated the wiki there (and will be synced to the wiki here also)

[BenWiederhake]

Awesome! It's good that you're back, I already got worried :)

[BenWiederhake]

Hmm, I can edit neither of the wikis, and I don't see an invitation notification. :(