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)