3D Flux measurement

[Christian Herenz]

Implement SExtractor MAG_AUTO in 3D.

Variant (a): Define the classical AUTO aperture in 2D - then extract flux over AUTO-like aperture in 1D.

Variant (b): Full 3D AUTO-like treatment... Need to figure out how that could work though...

[Christian Herenz]

Working variant (a) since fa30613 - this is what we now use for the first MUSE-Wide catalogue.