Require defaults for all X-scale ranges

[trisyoungs]

At some point we have lost the default values for all of the X-scale min/max/stepsizes. They could live as default values in our instrument definitions, but it isn't clear how these values would be applied to a file being loaded in from the user. We may have to just store the values as defaults in the relevant controls.

Can consult the original Java GUI for sensible numbers.