ParticleCollector: Prevented missing and duplicate collections

The particle collector was collecting some particles twice due to a
tolerance extending the tracked path. This has been removed. The new
tracking algorithm does not generate the same sorts of spurious
tolerance-scale motions that the old one did, so this extension of the
tracking path is unnecessary.

Some particles were also not being collected at all as they were hitting
a diagonal of the collection polygon and registering as not having hit
either of the adjacent triangles. The hit criteria has been rewritten. A
hit now occurs when the normals of the triangles created by joining the
intersection point with the polygon edges are all in the same direction
as the overall polygon normal. This calculation is not affected by the
polygon's diagonals.

The issue was raised by, and resolved with support from, Karl Meredith
at FM Global.

This resolves bug-report https://bugs.openfoam.org/view.php?id=2595