Consistent Handling of Emoji's in Messages

[49Indium]

I have noticed that there are a lot of regex variants to remove/ignore emotes from discord messages. These should be placed into a central function (maybe in command_utils.py).

Some examples:

• haiku.py: "<a?:.+?:[0-9]+?>"
• yelling.py: ":[\w\-\+\~]+:" (does links as well)
• cowsay.py: "<a?:\w+:\d+>"

Wow, if I had a nickel for every time I [found a regex for replacing discord emotes] ... I'd have two[three] nickels - which isn't a lot, but it's weird that it happened twice[thrice].

[andrewj-brown]

Closing as a subset of #120.