Habpanel not updating group switch state

[rossko57]

@andyh

This is a rather heavy handed fix, because it forces a complete download of all items.

Related discussion

[SOLVED] HABPanel sluggish

When switching dashboards HABPanel retrieves the whole list of items again (GET /rest/items) before displaying the widgets, this was a conscious decision to increase the reliability of the display, there were issues with state management when the SSE connection dropped at some point. This also gave opportunity for some widgets, notably the slider, to initialize themselves and perform initial rendering properly - they would display the wrong state or “flicker” for a split second. It was an accep…