Dashboard slideshow widget memory management

[renemarc]

As a user, I want my tablet interface to stay operational so that I can use the UI without having to restart it.

Acceptance criteria

1. It's done when any memory leak inside the slideshow widget is resolved.
2. It's done when Fully Browser Kiosk doesn't crash after the the Main dashboard is open for a while.

[renemarc]

Two workarounds are possible:

1. Use http-equiv="Refresh" header meta tag to force-reload the page on a regular basis
2. Use the Fully Kiosk Browser's Auto Reload on Idle feature.

To keep things universal, the first solution is used with a period of 1 hour.

[renemarc]

Reopening this issue due to random crashes still happening in Fully Kiosk Browser when slideshows are displayed.

For reference, the Auto Reload on Idle is set to 5 minutes, and no content is being cached.