Option to transfer, combine properties from peaks properties during merging step

[PMSeitzer]

Part of PeakContainer::mergePeakContainer()

If peak groups are merged, and there are multiple different peaks associated with a sample, the peak with the highest peakIntensity is chosen to represent that sample.

In some cases, it may be more accurate to merge the two peaks together, creating a new peak that collectively represents the sample. This would be a big deal for fields like rtmin, rtmax, peakArea and smoothedPeakArea, where one sample might split two structural isomers, while another does not:

However, in other cases, a tail peak might be picked with a prominent peak, and we would only want the prominent peak.

The easiest thing to do is to not try to merge properties, but this might be a useful thing to implement in the future (mostly for the structural isomer case).

[PMSeitzer]

came up during #686