Remove overlapping peaks

Resolves #282 (closed)

The functionality of the previous peak filter option "remove overlapping peaks" was flawed, since, it set the peak scale (aka peak end) to be 1.0 when testing for collisions between ellipsoids. This means that i) we the included region contains about 67% (1*sigma) of the points belonging to the peak, and ii) that it does not check whether the peak clashes with background integration regions of other peaks.

I have modified the Octree collision detection algorithm to check for collisions of a peak region (within _peak_end) with nearby background regions (within _bkg_end), and included this in both the peak filter subframe and the integration subframe. In the integration subframe, when overlapping peaks are removed, they will be marked as rejected, with RejectionFlag::OverlappingBkg.