Filter displayed elements in ElementPopup and ParamDlg

[coldfix]

Currently, the amount of displayed parameters is quite large and most probably not what a user wants.
A possible solution might to remove all parameters that have their default values, or better yet: collapse these parameters.

[coldfix]

The usage of ListCtrl for these dialogs opens new pathes for this matter:
It should be easy to add a button to hide/highlight parameters with default values.
On the other hand, this is matter becomes less important now, since the ListCtrl is less messy.

AT LEAST: put the non-null elements on top.

[coldfix]

Furthermore: highlight required parameters