Merge branch 'master' into function_fitting
Fix typo on Lorentzian in plugin.xml
Add Operators to plugin.xml
Add isValid() to IFunction and implementations

This is used by FunctionFittingTool to determine correctness of the
function tree. Also for functions which can be incorrectly configured
like JexlExpressionFunction it is quite valuable
Fix whitespace (remove embedded tabs)
New fitting constants for Function Fitting Algorithm
SCI-1740: Test and fix for Parameter.setLimits() incorrectly changing value
Merge branch 'function_fitting'