GSA_Toolkit: Add Spacers and properties

For fabric formfinding spacer elements are required to control the nodes within the fabric. This are arranged in the warp and fill directions with each line of spacers sharing a common property.

@rwemay has suggested using the framing elements and adding spacers as another type, it will allowing a collection of elements to be group in order for the same property to be applied. Also a spacer property will need adding to the BHoM.