add leap.mail requirement
Merge remote-tracking branch 'kali/bug/add-mail-dep' into develop
Add data_files under linux

* polkit file
* /etc/leap/resolv-update
Merge remote-tracking branch 'kali/bug/add-data-files' into develop
Move configured providers getter to LeapSettings.
Preferences: select enabled services for providers
Add changelog. Closes #3534.