Center point set before β-skeleton calculation

[szhorvat]

In β-skeleton calculations, when point coordinates are much larger than the typical inter-point distance, roundoff errors may become larger than the relative tolerances used to detect boundary points. This may affect the result: IGGabrielGraph[pts] and IGGabrielGraph[pts + 100000] may produce slightly different results.

One possible workaround is to shift the point set so it is centred around the origin before performing the calculation.