Create a 'vector' entity to use in teaching 3D Math

[PhilipRosedale]

This is the starting point for a teaching tool to help visualize vectors and rotations in 3D.

Create two linked primitives - a cylinder and a cone, about a meter long, so that they form a 'vector' object that can be grabbed and positioned or resized, also create a text entity that is always above the vector, which contains text giving the length of the vector (in meters). When the vector is grabbed and moved or resized, update the text using an entity script that is triggered by mouse or near grab.

Submit this to me as a PR in this repository.