Update "# licensed days left" at midnight.

[RealRaven2000]

For those users who leave Thunderbird running for multiple days, update the label of the quickFilters button so they know in advance when their license may run out.

Currently this label is only updated when the Add-on restarts, is updated or Thunderbird starts up.

[RealRaven2000]

Implemented in 5.9.2 - published 25/06/2023