Summary: Current code only supports one player
Test Plan: Run two media sessions. Dbus inspection works fine, UI has some issues with values not updated, but out of scope for this diff
Reviewers: #kde_connect, apol
Reviewed By: #kde_connect, apol
Subscribers: apol, #kde_connect
Tags: #kde_connect
Differential Revision: https://phabricator.kde.org/D12546
