Use material icons in MPRIS activity
Summary: The previous icons were old (pre-Material, maybe even pre-Holo). The recommended practice now is to add the icons directly to your app, so I added the material icons. Note that the vector version is used; these are automatically converted to bitmaps for older android versions.
Reviewers: KDE Connect
Differential Revision: https://phabricator.kde.org/D8955