Add function + enum to check element geometry

i.e. either T or Q
BrickFromTetMesh requires nnode1d=3: add paranoid check
In FullCircleMesh add paranoid check of input sizes

Mesh constructor can only generate meshes of 5 elements, so the size of
the input vectors must be 4. This was not checked anywhere in the code,
and trying to create more refined meshes by adding new "theta_position"s
resulted in singular elements.

Added a paranoid check to stop other people wasting time on this.
Allow OneDMesh to be used with T elements

(it works fine but the paranoid check stopped it)