Import additional information from SNS nexus files

[AndreiSavici]

This ticket is blocks : TRAC10428

One might want to get information about a run without completely loading it. The following information is missing from the workspace logs:

• das.neutrons - might want to overwrite it after filtering (in http://trac.mantidproject.org/mantid/ticket/10428)
• das.protoncharge already gd_prtn_charge
• das.runtime already duration
• das.monitor2counts, das.monitor3counts - might want to update it if you do something to monitors (filtering, cropping, etc) (in http://trac.mantidproject.org/mantid/ticket/10428)
• Sample description
• Experiment identifier
• Notes already file_notes
• users (in http://trac.mantidproject.org/mantid/ticket/10428)

[AndreiSavici]

This issue was originally trac ticket 9392