Support changing list shortcodes/local overrides

[deepbluev7]

Is your feature request related to a problem? Please describe.
Shortcodes are hard to remember, there is no easy way to list them and they are global.

Describe the solution you'd like
I would like to be able to make the shortcodes easier to read on my end. I.e. rename the matrix tos list to matrix.org-tos and similar. It would be nice if that could change the global default or be a local override depending on my preference.

Describe alternatives you've considered
You can manually edit the name and tell everyone to !sync, but that is still global and I can't do that for lists I don't control.

Additional context
Related to #41

[ShadowJonathan]

Plus, and i'm fairly sure the code doesn't prevent this, to have mjolnir deny watching a list if its alias already exists in the watched lists.