Make mail fetch interval in imap service configurable

using environment variable.
Closes: #3409
Use DELETE /1/logout to properly logout
Remove mock dependency since it's no longer needed.
update coveragerc to bitmask namespace
Merge remote-tracking branch 'chiiph/bug/properly_logout' into develop
Merge remote-tracking branch 'kali/feature/3409_make_imap_poll_configurable' into develop
Merge remote-tracking branch 'kali/bug/remove_mock_dep' into develop
Merge remote-tracking branch 'kali/bug/update_coveragerc' into develop
Fix logout test
Merge remote-tracking branch 'chiiph/bug/fix_loguot_tests' into develop
fetch incoming mail when mail client logged in
Merge remote-tracking branch 'kali/feature/3525_login_triggers_fetch' into develop
Make username lower case before using them
Merge remote-tracking branch 'chiiph/bug/lower_case_username' into develop
update versioneer version
Rebrand the latest bits
Merge remote-tracking branch 'kali/feature/update_versioneer' into develop
Merge remote-tracking branch 'chiiph/bug/manifest_rebrand' into develop
Remove unused resources path.
Add preferences panel.