Add Primitive meshes to the default system resources

[jayrulez]

Add primitive meshes (Cube, Sphere, Cylinder, etc...) to the default system resources.

Alternatively, make it possible to easily generate these meshes as part of the mesh creation process.
Instead of selecting a mesh from the file system, there could be an additional option to select the source of the mesh.
The options would be Primitive and File.
If File is selected (the default option), then everything works as it does currently.
If Primitive is selected, then the field for the file path is replaced with a drop down list of available primitive meshes.
When a primitive mesh is selected, it this will automatically, it will automatically populate a default material.