Enh: UI - missing buttons if no emails are displayed

[sebbASF]

The buttons to (un)subscribe, post and maintain favourites are not displayed unless there are some emails that fit the criteria (e.g. last month).

This avoids dealing with missing or inaccessible lists, but it makes some actions harder. In particular removing a favourite or unsubscribing from list that is no longer active.

The code should be able to check if the user has access to at least some of the messages on the list and display the buttons if so.