Make it user-specific

[dartiss]

Would be nice to have an additional option to specify per-user as well.

So, there will be settings in both the General Settings and User Profile as well.

In both cases, there will be a "None" option, allowing the other to override.

General / Theme -> User / Theme = User theme
General / None -> User / None = No theme
General / Theme -> User / None = General theme
General / None -> User / Theme = User theme

Look at using edit_user_profile and show_user_profile hooks for adding the content to the user profile. Then use get_the_author_meta to get the details.