* ui lua integration: added doLayout to model and text node

* model and text onLoaded methods contained code to do layout related
* checks and pre-computing -> these were moved into doLayout since this
* is the correct place for these actions

* this removes warnings when lua creates nodes wich are not yet setup
* correctly
* ui lua integration: fixed checkbox issue (second try)

* problem with the checkbox was actually related to the allocation/cloning
* strategy of nodes in combination with the use of reference vars in
* abstractvalue nodes