Modify LoadDetectorInfo algorithm to understand detector.nxs files

[abuts]

Detector.dat file describes modified detector's positions which replace Instrument description or raw file's detectors positions with the positions, calculated from a calibration procedure.

Unfortunately, it is an ascii file, which has to be read at each reduction step. This takes substantial time.

In addition to that, there are some cases (e.g. maps) when the detector.dat file is not availible and nxs file with specific format is provided instead.

The purpose of this ticket is to modify LoadDetectorInfo algorithm to understand this kind of nxs files too and modify the detector position/time of flight on the basis of such files.

[abuts]

This issue was originally trac ticket 6543