Add Default Commands to Custom Commands, allow modification

[Marstead]

I have a lot of trouble with some of DeepBot's default commands and would like to be able to edit them. Change their permissions, disable them entirely, or otherwise adjust how they function. Some commands can be overridden with an identically-named custom command, but this doesn't work for every command (!add, for example) or in every use case (whisper or Discord commands).

I think a lot of the one-off issues with default commands could be fixed if these were simply populated automatically in the Custom Commands module under special group "default". Each default command could have a "Revert" button that restores the out-of-the-box functionality, and a warning if a user attempts to edit them.

[Marstead]

This would remove a lot of the clunky need for customization on these commands elsewhere in the app, such as in the Master Settings module where we can customize currency command text. Instead of needing these separate customization areas, it could all be done within the custom commands module.