Customizable ventilation grid

There is a newer Version available with many more possibilities - see: https://www.thingiverse.com/thing:5188211
========================================================



This ventilation grid is a remix of Thing https://www.thingiverse.com/thing:3115753

I added the possibility to change the witdh in addition, not just length and diameter.

Now its possible to create also rectangular ventilation grids in a wide range of grids and sizes.
Also I changed the parameter names to english and added the valid parameter range to each parameter.

Version2 works better together with the Thingiverse customizer. It also uses clearer naming of the variables. In addition V2 outputs errors on the console, if parameters are out of range.