Allow 3DRepo to receive objects that do not have a Mesh Representation

#### Description:

Unlike Speckle, 3DRepo can only receive mesh objects. Any metadata has to go attached to a mesh object, which is why we need to compute a mesh representation then attach BHoM data to it. This is similar to Speckle, but you always need a "parent" mesh object, whereas in Speckle you can also send directly a Custom Object with no parent mesh.

To solve this, we might simply create a Mesh container – e.g. a tiny one-faced mesh, centered in the origin – that will be the container for all of the BHoM objects that do not have a representation yet.