Show date of last successful filter list download

Background

In case a filter list download fails, an error is shown in the options page but not when the download last succeeded. As mentioned in https://issues.adblockplus.org/ticket/2848 we could add this information as a tooltip on the error message or expose it through other ways.

What to change

In case a filter list download fails, we should show the date of the last successful download at the following position:

  • current options page: to the right of the error message
  • new options page: in a tooltip when hovering over the error message
Edited by Thomas Greiner