Fit dialog UI improvements

[mantid-builder]

This issue was originally TRAC 7580

Original Reporter: Arturs Bekasovs

When no functions are added to the Fit algorithm dialog, it does what is expected - shows an error message not allowing to submit the dialog. However, no red star is shown any close to the functions panel, so it might be difficult to determine what the problem is.

Additionally, when all the previously added functions are removed from the dialog, it is not showing any errors when submitting it and is somehow using removed functions in calculations.

[mantid-builder]

@NickDraper (2014-02-14T11:07:59):
bulk move to assigned at the into of the triage step

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