[Task] Checklist before deploying v0.4.0

[No767]

Task Description

Targeted Release Date: Nov 26, 2022

Here's a list of stuff that needs to be done before Kumiko v0.4.0 goes live. This list will be changed and new ones will get added later on

• [x] Audit all economy commands
• [x] Audit all additional commands (not from Rin)
• [x] Globally roll out all slash commands
• [x] #158
• [x] #157
• [x] Update Docs
• [x] Fix unbanning user issue
• [x] Add a global error handler for no permissions
• [x] #160
• [x] Rely on user perms and roles instead of bot perms for admin cmds
• [x] #162
• [x] #167
• [x] #172
• [x] Clean up code layout
• [x] DB migrations for MongoDB (check Beanie's docs) (This can be only used on replica sets, which Kumiko does not use)
• [x] Remove unused coroutines for eco package

[No767]

oops made a mistake. should be #160 not #159

[No767]

still in the process of fixing up bugs