#13 Make appropriate fields use the EmptyBoundedIntegerValue

[Declan McGrath]

Make appropriate fields use the EmptyBoundedIntegerValue.

This will have to be thought out a bit better. Basically we want to use a consistent constant across the application for describing an empty value.

This will require us to look at the range of values we use for each data field and seeing if there is a value that we can use - ie. a value that will lie OUTSIDE the range of values for all data fields.