Make 'All Accounts' feature more aware

[devmount]

Is your feature request related to a problem? Please describe.
The select option for 'All accounts' can easily be overseen if only using one activated account.

Describe the solution you'd like
Add a note to the accounts option on the options page that multiple active accounts activate the 'All accounts' option.

Describe alternatives you've considered
It's also possible to always show 'All accounts' select option even for one single account and deactivate it if only one account is activated. This can be implemented in addition to the proposed solution.

Additional context
#273 (comment)