Fix peaks option to remove non-monoisotopic peak groups

[PMSeitzer]

In the Peaks dialog, there is an option to determine if a peakgroup is monoisotopic or not ( the "Require Monoisotopic" checkbox).

The algorithm is implemented in PeakGroup::isMonoisotopic() and Scan::isMonoisotopicPrecursor().

This appears to be completely broken, and needs to be reimplemented/revisited.

This was discovered from #746, and the option has been disabled/removed from the dialog.

[PMSeitzer]

From Neg_standards_yeast_background_30_yeast_07.mzXML:

[PMSeitzer]

Clearly, these two peaks are not isotopes of one another (note the shift in RT).

[PMSeitzer]

Once the option is fixed, it would be good to add this option to peakdetector