Refs #8777 Add default values to FuryFit.

This also adds logic to update the Intensity/Background parameters to always sum to 1.
Refs #8777 Update with a better value for tau.
Refs #8777 Plot guess after switching function type.
Refs #8777 Constrain range to be between 0 and 1
Merge remote-tracking branch 'origin/feature/8777_furyfit_default_values'