Convenience functions and bug fixes!

magdata: added convenience functions for flipping and rotating of magnetic
         distributions, fixed bug with ar_dens.
phasemap: now also has a mask which will be used to construct a 3D-mask for the
          magnetic distribution during reconstruction. Added setter/getter.
          Added copy(), scale_down()/scale_up() convenience functions.
          !CAUTION! Only NetCDF4 files save every new parameter!
projector: Fixed hidden bug in X/YTiltProjector, which was problematic during
           tilts over 360°. Now uses linear algebra (much clearer!).
           get_info() function now can be used non-verbose (for filenames).
dataset: added several setter/getter, addes set_3d_mask() for simple 2D tasks,
         renamed mask to confidence (for Se_inv construction)
tests: updated to include the fixes and new functions introduced in this update!