Refs #10090. POLDI chopper speed is rounded to next 500
Refs #10090. Refactored chopper parameter loading process.
Merge branch 'master' into feature/10090_correct_poldi_chopper_speed
Refs #10090. Added extractor for chopper speed target

As it turns out, the chopper speed target is stored as integer list, so the value needs to be converted.
Refs #10090. Added POLDI definition 2014b

The instrument definition is required for the adjusted system test.
Merge branch 'feature/10090_correct_poldi_chopper_speed' into develop