User Manual: Exception Handling in genie_python

As a scientist, I want to understand how to use Python exception handling with genie_python, so that I can write genie_python scripts that are capable of handling exceptional situation that might be encountered in experiments.

#### Acceptance Criteria
1. Examples of how to use Python exception handling in genie_python scripts in the user manual

#### Notes
1. This ticket arose from the genie_python presentation to scientists. They asked if genie_python had any feature resemlbing OpenGENIE's Ctrl+C handler.
1. genie_python does not have a direct equivalent of OpenGENIE's Ctrl+C handler. There is little point in creating one, because Python has much more general exception handling.
1. It would be much better to demonstrate to scientists how they can use Python exception handling to achieve the same end.
1. Two examples would be good. Three or more examples would be even better.