Migrate from PreferenceActivity to PreferenceFragment because it has been deprecated since Android 3.0 API11
Summary:
PreferenceActivity has been deprecated since Android 3.0 API 11 in favour of PreferenceFragment
Test Plan:
Apply patch and observe that the DeviceSettings and PluginSettings screen behave as expected
and now also follow material design guidelines
Reviewers: KDE Connect, nicolasfella
Reviewed By: KDE Connect, nicolasfella
Subscribers: kdeconnect
Tags: KDE Connect
Differential Revision: https://phabricator.kde.org/D17859