Implement message length cap

[tfuxu]

Implement a check in message composer that will inform user, that the message length cap has been reached. Currently as a feedback, user gets a technical error below their message, which isn't ideal.

For non-Nitro users this will be: 2000 characters; And for Nitro users: 4000 characters.

Current indicator:

_{Message says: The length of the message must be no more than 2000 characters.}

[tfuxu]

Also, if user would still try to send a message, we should display something like this: