Refs #9432. Cleaned up PoldiPeakCollection and PoldiFitPeaks1D

Some functionality has been transfered from PoldiPeakCollection to
PoldiFitPeaks1D, as it was too closely linked to PoldiFitPeaks1D. For
PoldiFitPeaks1D there are some unit tests now, but a system test will be
added to make sure everything works properly.
Refs #9432. Added unit test for PoldiFitPeaks1D properties