Added New functionlity for length grid

Default Variants:

We can now setup default variants, these can be filled in on the item card in the field default variant code. If this field is filled in then based on the default variant code lines the item variants are created for this item. 

In the default variants the different types can be setup. By selecting the lines action the specific variant setup can be done.

In the default variant lines the user can quickly setup the variants settings for length. The fields for width, thickness and diameter are hidden by default. With the edit action the default variant card is opened.