User experience improvements for reactor source experiments

[AndreiSavici]

As part of testing ticket http://trac.mantidproject.org/mantid/ticket/10929 I have found a few things left to improve

1. LoadSpiceAscii should not require dat time format
2. ConvertSpiceDataToRealSpace creates an MD workspace with Y min and max limits both 0
3. ConvertCWPDMDToSpectra is a weird name. It should at least be explained in the documentation
4. Binning parameters must contain 3 numbers. People might be used to Rebin, that can also use one value. Minimum and maximum can be calculated
5. There is a weird warning message "Unable to set unit to an Unit::Empty object." The reason is that the "Degrees" unit is not registered.
   Changes:
   a) Code/Mantid/Framework/Kernel/inc/MantidKernel/Unit.h, line 616, replace

{ return ""; }

with

;

b) Code/Mantid/Framework/Kernel/src/Unit.cpp add line 1121

DECLARE_UNIT(Degrees)

c) fix code in Code/Mantid/Framework/MDAlgorithms/src/ConvertCWPDMDToSpectra.cpp about Twotheta to

pdws->getAxis(0)->setUnit("Degrees");

[AndreiSavici]

This issue was originally trac ticket 11282