Pixel ID should follow time-of-flight in the event structure - not the
other way around.

Refs #5367

Also added a diagnostic print to show off what the difference in the
number of masked spectra versus detectors.

Fixes the problem of only ignoring OutputWorkspace_ properties so it was
returning the additional MonitorWorkspace properties. It now does
not return any property with an underscore in the name.

One of the loaders that SNS supports, LoadEventPreNexus, does not use the
Filename property. Therefore, I've made a way to set that.