Fix MPRIS pause

Summary:
BUG: 390010

According to the MPRIS spec (https://specifications.freedesktop.org/mpris-spec/latest/Player_Interface.html) the value of canPause should not depend on whether the track is currently paused. This patch makes Elisa behave
according to the specification and makes it controllable via KDE Connect

Test Plan: Inspect via DBus Viewer and KDE Connect

Reviewers: Elisa, astippich

Reviewed By: Elisa, astippich

Subscribers: astippich, Elisa

Tags: Elisa

Differential Revision: https://phabricator.kde.org/D11020