action_items: add reactions

[wizzdom]

Closes #57

• Adds ✅ reaction to each action item message
• Once one of the users mentioned in the action item message reacts the message is edited, crossing it out and adding a checkmark

NOTE: I have no idea what I'm doing, there is definitely a better way of doing this, This was put together from boosts.py and stumbling through the hikari docs.
Some sort of hooks here might work, along with a better way of verifying the user and bot ids.
I have not tested role ids and its probably half broken ❤️

[novanai]

There's a few last issues with this that I'm working on

[novanai]

Tested, working perfectly