Resend ItemAdded events on reset instead of readding items

[jliersch]

Situation

In order to reset the simulation, various envire items are removed and readded from/to the envire graph. This involves creating copies and multiple searches for the same items. Avoiding this may speed up the reset of the simulation and also reduce potential data fragmentation.

Task

Instead of readding the items to the graph, for each relevant item notify the envire plugins about the need to react to adding the item to the graph again without actually readding the items.

[jliersch]

This may require extending the EnvireGraph in envire_core with a suited method.