Refs #6616. Specialized property manager for parameters

It is currently a regular QtDoublePropertyManager, so nothing the fit
browser should still work correctly. It gives me a way of overriding the
manager for parameter properties only, leaving other double properties
alone.
Refs #6616. Specialized version of property manager for parameters
Refs #6616. Implement error setting and proper displaying

Still a few things to do, but the basic functionality works perfectly
Refs #6616. Specialized on-change function for parameters
Refs #6616. Clear parameter error when the value get edited
Refs #6616. Make error setting to update the parameter display

Remove some unnecessary constness as well.
Refs #6616. Set error values only when actual fit was done
Refs #6616. Remove constness from error map
Refs #6616. Make it possible to turn error display on and off
Refs #6616. Add the new option to the Muon fit browser
Refs #6616. Clear errors when doing undoFit

Plus some code refactoring to avoid repeating myself
Merge branch 'feature/6616_muon_error_in_fit_browser' into develop

Conflicts:
	Code/Mantid/QtPropertyBrowser/CMakeLists.txt