Add click to play/pause feature on previews for audio/video

Test Plan:
In dolphin, click on a video or audio preview in the information panel.
The video or audio preview starts

Reviewers: elvisangelaccio, #dolphin, ngraham

Reviewed By: elvisangelaccio, #dolphin, ngraham

Subscribers: alexde, anthonyfieroni, ngraham, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D22183