Further steps as defined below

 1. Change the filename reported for nexus files if xml contained within
 1. Stop saving the filename to nexus processed files
 1. removed some unused includes

Still to do:
 1. cache SHA1 checksum if needed
 1. Manually test
 1. update documentation
 1. investigate this error:

ctest -C Debug -J 4 -R LoadEventNexusTest -V

 548: LoadParameterFile-[Error] Bad path syntax: C:\Mantid\Code\Mantid\instrument
\C:\Users\rrc79113\AppData\Roaming\mantidproject\mantid\instrument\HYSPECA_Param
eters.xml. Unable to parse File: in C:/Mantid/Code/Mantid/instrument//C:\Users\r
rc79113\AppData\Roaming\mantidproject\mantid\instrument\HYSPECA_Parameters.xml
548: LoadIDFFromNexus-[Notice] Instrument parameter file: C:\Users\rrc79113\AppD
ata\Roaming\mantidproject\mantid\instrument\HYSPECA_Parameters.xml not found or
un-parsable. Instrument parameter file: C:/Mantid/Code/Mantid/instrument/HYSPECA
_Parameters.xml has been loaded

re #11818