Calculate geometry

[toqduj]

WIP Adding a geometry calculator that would calculate for each pixel:

• Q (=sqrt(|Q0^2 + Q1^2 + Q2^2|),
• Q0,
• Q1,
• Q2 (=0 for now),
• Theta (half scattering angle),
• Psi (azimuthal angle), and
• Omega (Solid Angle)
  When possible with uncertainty estimates. This assumes that the data dimensions follows [..., ..., (Q2,) (Q1,) Q0]. rank_of_data of 0, 1, 2, indicates whether we use 1, 2, or 3 dimensions for our data. The remaining dimensions are assumed to be dependent on external variables such as frames, temperature, position, etc.

Needs some thought, though. For example, for a Mythen strip detector data read-in, we actually use dimensions of [1280, 1] and a rank_of_data of 2, as we have finite size pixels...