LoadDetectorInfo now just loads parameters & adjust det positions

Refs #8640
Move MARI det parameters to instrument level

This helps the performance of the LoadDetectorInfo algorithm.
Also fixed a spelling error in LET_Definition.xml comment
Refs #8640
Swap out UpdateInstrumentFromFile for LoadDetectorInfo

This will allow users to overwrite the delays/pressures/thicknesses
if required.
Refs #8640