Add a Counter to Show how often each command is used

The number of commands is increasing rapidly. Perhaps adding some metrics would be helpful. These metrics could include how many times a command has been used and the last time it was called.

This could be used by Bot Admins to identify unused commands. Then they can try to improve the command to make it more useful or deactivate the command to "de-clutter" the !commands list.

The issue names no files, tests, or entry points. Start by locating the command handling and command-list code, then determine where usage counts and last-called times could be recorded; done means Bot Admins can identify unused commands from those metrics.

Written by the indexing model from the issue text.