Additional parameters on Loading run files

When loading a data file with LoadMuonNexus, it returns a workspace plus various other details such as the grouping, dead time table, time-zero, first good data, etc. These values are only available from LoadMuonNexus, so re-running an analysis script often requires it to reload the data from the archive even if the workspaces are still in Mantid’s ADS memory.

It would be useful if these additional values are also attached to the workspace in some way so they can be extracted. And (for example) ApplyDeadTimeCorr() can now make its dead time table input optional, defaulting to the one stored in the raw data. Maybe even Fit() can use First Good Data if StartX is not explicitly given?