v0.7.88 - Bug fix. Minor feature. 3 camera limit for playback mode.

* [0.7.88] - outputImageStillModern() now adds data-monitorid attribute
and filters out any non numeric characters.
* [0.7.88] - playback.css styling changes
* [0.7.88] - playback.js 3 camera limit for playback mode introduced to
improve stability for lower spec machines. A toggle to disable this will
be included in a future release.
* [0.7.88] - playback.php minor change - outputImageStillModern
parameters brought up to date