Bugfix + solid angles match conditions relaxation

Fixed major bug: looks like layer thicknesses along Z-axis were
calculated incorrectly if the x component of the sample orientation
vector was /= 0. Must have been noticeable with very thin and light
samples.

Based on request by Matthew Wormington: the conditions that check if
solid angles should be recalculated have been relaxed a bit, by looking
at the extremes of the layer system along the Z-axis.

The detector position and normal vector still have to correspond though
Bugfix: save button behavior when launching simulation