Change the /editmessage command to just rewrite the get-roles-message

[CarrotManMatt]

There seems to be very little purpose for a committee member to manually enter the text to replace a message that TeX-Bot has previously sent. Instead every command that can create a new message by TeX-Bot should have an edit boolean flag, along with the ID of an existing message, to rewrite the text defined originally for that message.

There will be no need to replicate the message text once #90 is complete.

[CarrotManMatt]

Or in the case of the /writeroles edit:True the message_ID flag should actually be message_IDs which is a tuple of messages to replace