Support for installation and update of ScriptRepository

Add support for cloning and updating the local repository when using the
ScriptRepository interface.
re #6175
refs #5849 filename made class parameter trying to fix problem

on build servers
refs #5849 enable all disabled tests

as seems the previous commit have fixed all problem
refs #6315 fix problems found during migration.

1) Fix the problem with warnings being emitted as a result of duplicate calls to connect.
2) Fix problem with ThresholdRange objects, particularly MedianAndBelow.

There is still an outstanding problem with the non-axis aligned binning plugin that I need to fix.
refs #6275. Added help link.
Refs #6385 only set variable if using nx
Re #6452. Breaking an infinite loop of resizing and drawing.
Re #6430. Make the algorithm fail, not crash, for table workspaces.
Refs #5428 Make use of PhysicalConstants::meVtoKelvin

modified:   ../inc/MantidAlgorithms/SassenaFFT.h
modified:   ../test/SassenaFFTTest.h
Fix typo. refs #6096
Re #6253. Don't run filtering methods if working with histogram data.
Fix ID ordering of first two elements in det table Refs #6262

It turned out to be an undefined order in which the iterator was being
incremented and dereference in a chained function call.
Validate workspace box in LoadDialog when widgets created. Refs #6442
Re #6451. Redrawing picking image every time made it slow.
re #6194 caught a couple of straggler sub algorithm references
Refs #6185 throws for unsupported file type
Refs #6185 change wiki and optional message strings
update to polaris idfs. re #6310
remove mark-as in new polaris idfs. re #6310
Couple more mark-as removed. Re #6180