Unique element ID is reset #519

Using {{ id }} in an element sets a unique ID for every element (such as fred_313846b_zfe29zitrc ID2: fred_313846b_zfe29zitrc).

This is very useful for accordions for example.

However, rebuilding elements resets all ID:s to an identical value (8 in my case). To make the ID:s unique again one has to resave the resource.