[Permissions] Allow all commands to be allowed/denied in a channel

#### Select the type of feature you are requesting:

- [x] Cog
- [x] Command
- [ ] API functionality

#### Describe your requested feature

A similar feature already exists in core with the [p]ignore command, however red responds to commands from users with discord manage channel and server permissions. With this feature implemented the bot owner or admin(s) could deny an entire channel for people with the above discord permissions. If this were added I expect it would look something like `[p]permissions setdefaultserverrule `.

A different way to implement it would be to be to add a method of referencing all of the bot's commands as one cog, such as "All". If this way was chosen the current syntax for the command would still be entirely valid.