Decide how we should add descriptions to things

[coretl]

We need to know descriptions at multiple levels of the heirarchy:

1. When looking at a PVI screen for a motor or camera driver we would like to have a description of what it is/where it is
2. When looking at a component like a DCM/camera we would like to have this information too
3. When looking at an IOC we want to know what is within it

We would also like summary screens (like the all motors one) to have this information

This ticket is to work out how we get this.