Datetime filter for layers to allow for automatic, time-based publish/unpublish

[FredrikEkstrom79]

Whould be nice to have two new fields to type start and end date for when a layer i avalible in current map.
In the picture i have drawn in the layer under map-config but you might want this directly under layer also and under map so you can override this setting per map basis.

The layer in marked with a symbol to mark that the layer will not avalible/visible if its loaded in now in a map.

It's just a idea i hade about a "simple" date-filter. We can disscouce this more...