Add definition of shape to intrument definition

[NickDraper]

This needs to be done in partnership with Sri.

We need to add xml to the instrument files to define the shape of the base level types.

This needs to start with a discussion between Sri, Anders and Nick.

I suggest that we hide the fact that we are using infinite surfaces in our definitions, and provide user friendly tags for common objects.

```
`<Cylinder id=“Bertie” radius=2 cap1=“4,5,6” cap2=“1,1,1”/>`
``
``
```

[NickDraper]

This issue was originally trac ticket 194