refs #8557 Two questions to 2 suspicious places of code

Two places found after code review which look like wrong. Questions to code were placed after //!!! mark
Merge branch 'master' into feature/8557_SNSvsISIS
refs #8614 Should fix the issue.

Though careful checks are needed. (and system tests as well)
refs #8614 temporary reverted changes

as they cause strange behaviour

Revert "refs #8614 Should fix the issue."

This reverts commit a41f3e45c2a0abbe6a1c9f93f9a26d6140265ad8.
refs #4614 here the changes brought back again
refs #8614 trying to nail down reason for MARI tests failing
refs #8614 Now it works as expected for LET

and changed LET_Parameters.xml to have default nexus files to be nexus, not event nexus files.
refs #8614 Minor comments
refs #8614 Removed unnecessary parameter in instrument definition file

Generic loader now distinguish between nexus and event nexus file.
Merge branch 'master' into bugfix/8614_letReduction
refs #8614 Dealing with consequences of ill defined merge

Some code pieces came not valid
Refs #8723 add LoadIsawSpectrum algorithm
Refs #8723 add LoadIsawSpectrum algorithm
Refs #8020. Change loading code to use temporary workspace.

Temporary workspace is not in the ADS. When loading/correction/grouping
are finished - temporary workspace is added to the ADS replacing
MuonAnalysis and MuonAnalysisGrouped.
Refs #8020. Remove redundant method.

We do not delete ranged workspaces as we are no longer storing them
in the ADS.
Refs #8020. Re-enable support for a range of workspaces.
Refs #8020. Fix DTC of multi-period workspaces.
Refs #8020. Fix problem with groups not being replaced correctly.

ADS::addOrReplace is not replacing groups properly, which clutters up
ADS quite badly.
Refs #8020. Fix groupWorkspace() to handle ws which are already in ADS
Refs #8020. Make it possible to load after loading error.