ReflectometryReductionOne should correct positions

[OwenArnold]

This ticket is blocked by :

• TRAC9389
• TRAC9401

This is a simple principle: If you have known incident theta angle, and a reflection condition, i.e. theta_in == theta_out, then you can correct the detector positions accordingly.

I've avoided this problem so far, because for the multi-detector case you may have a number of 'masked' pixels, in which case there is no easily identifiable vertical centre position.

Having had a chat with Tim about this, we've agreed that if you have a range of pixels in the processing instructions, you should find the centre location and use that, along with the theta position to correct location. Corrections should still be optional.

Changes should apply to ReflectometryReductionOne, ReflectometryReductionOneAuto, CreateTransmissionWorkspace and CreateTransmissionWorkspaceAuto.

As part of this. We should also update ReflectometryReductionOne (following http://trac.mantidproject.org/mantid/ticket/9401) to calculate The OuptutTheta value if Multiple Spectrum numbers are given instead of component names.

[OwenArnold]

This issue was originally trac ticket 9184