LoadEventNexus (+ LoadNexusMonitors and other LoadNexus...) cleaning/maintenance

[Federico M Pouzols]

While working on #8990, #9248, #10595, I saw a few suspicious points:

• error checks and messages are not very good, reflecting also that the code structure is a bit messy
• some chunks of code are probably duplicated
• it seems that questions like "has this file any event data?" are tested in different ways in different parts of the code and different algorithms
• the documentation seems outdated/not to say all the truth. It is not clear what is the support status for SNS and/or ISIS files, although both seem to be well supported in principle
• It might be worth to have a look at how well these algorithms are covered by the system tests

These and possibly additional points need to be clarified and corrected if needed. It definitely looks like the set of Nexus loading algorithms should be better documented and/or harmonized.

I'd start by reviewing/expanding the tests. The description of this ticket may change as we clarify what needs fixing.

[Federico M Pouzols]

Note that LoadEventNexus' doc says "NeXus files (produced by the SNS)" even though it is definitely able to load ISIS files too. This needs to be clarified.

[Federico M Pouzols]

I just found an old related ticket: #8172. Add the issues described there to the list of points to check here, and close that ticket when this one is done.

[Federico M Pouzols]

It seems that I removed the 'blocked by' inadvertently.

[Federico Montesino Pouzols]

Clarify that this is not SNS specific, re #10619

This definitely works with ISIS files, so the old text can be very confusing to users. For now, keep it as "works with SNS and ISIS", as it was done for the LoadNexusMonitors doc, as it is not clear if it works for others / is generally applicable.

Changeset: 09cf32c66907567d8f3167a6d9927de656228d62

[Federico Montesino Pouzols]

Clarify that this is not SNS specific, re #10619

This definitely works with ISIS files, so the old text can be very confusing to users. For now, keep it as "works with SNS and ISIS", as it was done for the LoadNexusMonitors doc, as it is not clear if it works for others / is generally applicable.

Changeset: 9b2e5e08f4db2490cdad1c6ee058ef8cc7eba47b

[Federico M Pouzols]

Note: NeXus IO has been much improved for table workspaces recently: #10123.

[Federico M Pouzols]

Another related ticket: #7523, inconsistent behavior of spectra filtering in LoadNexusProcessed.

[Federico M Pouzols]

One more: #8175, clarify status of deprecated versions of LoadXXX algorithms (especially LoadISISNexus).

[Federico M Pouzols]

Added a couple of Coverity tickets that come with a bunch of Nexus, Instrument, Logs, related issues.

[Nick Draper]

Moved to R3.5 at the R3.4 code freeze

[Stuart Campbell]

This ticket has been transferred to github issue ​11461