Update tomo

Update the tomo code. Changes:

• wrap AstraData and AstraAlgorithm to let the garbage collector handle (possibly GPU-) data allocated by astra
• verify and document geometry
  • tomo angles measure the rotation of the sample in radians around the axis pointing up (opposite of astra convention)
• reduce duplicated code. for example fanflat, fdk, sirt3d, iradon_parallel and parallel3d have been combined into tomo
• extend reprojection alignment with optional binning, in general reproduce usability of the holotomotoolbox -> no longer wanted: bining should simply be applied prior to reprojection alignment
• registration of shift and rotation between two images is now possible

other decisions:

• enable linking data (instead of copying), but do not do it by default, as things can get messy if you e.g. load projections by linking, later do a backprojection and have the original projections change.