Phase offset and ramp can now be fitted! Many updates and fixes to plotting!

colormap: New module with colormap subclass which has special functions to
          calculate directional rgb-colors, now used in many plots!
__init__: On star import now also has abbreviations for a few modules.
fwd_model: Now has flags for fitting an offset and/or ramp.
           CAUTION: will be moved next update to new class!
magdata: Removed colorwheel stuff (all moved to 'colormap'). Overhaul of quiver
         plot in 2D and 3D. Now shows mask and uses new colormap for angular
         color coding.
phasemap: Now uses the new colormap for holo plots. Removed color wheel (moved
          to the new class). Added function to add ramps.
phasemapper: Now handles also offsets and ramps in the phase.
             CAUTION: will be moved next update to new class!
projector: Fixed bugs in SimpleProjector. 1) leftmost pixels are no longer moved
           moved to left corner of padded projection (when dim_uv is not None).
           2) odd padding when using dim_uv are now handled properly (one more
           pixel on top and right if necessary).
costfunction: n is now taken from the fwd_model instead of the data_set.
dataset: Introduced the count variable which gives the number of images.
magcreator: In the process of updating, more on next commit.
reconstruction: Also handles ramps and offsets now, properly extracts them after
                reconstruction.
regularisator: New argument 'add_params' is used to cut off input (for offset
               and ramp) which are not used in the regularisation.
scripts: several small changes...