Fixed a lot of small bugs. Removed the plotting routines from most of the spaces.
Fixed furthermore: - Let's undo the changes in the RGSpace.__init__ (see the comment on gitlab) - The HPSpaceParadict still has `distances` in the list. - HPSpace.copy: Is this method really necessary? The one from Space should be sufficient, right? - HPSpace.total_volume is missing - Unnecessary imports of `random`, `LMSpace`,... in hp_space.py - I removed the plotting functionality from the space classes. - GLSpace.copy should also not be necessary - GLSpace.dim is missing - GLSpace.vol should be called `total_volume`. Also its implementation is defect: there is no self.distances for GLSpace. The total volume is just 4*pi. - Use nifty_utilities.cast_axis_to_tuple in order to sanitize `axes` input in GLSpace.weight - typo in `new_shape = np.ones(x.shape)`