Implement 3D features for PlotHelper and add 3D scatter plot

This MR

• adds 3D plotting functionality to the PlotHelper
• adds the 3D scatter plotting capability
• fixes a small bug suppressing the creation of a 3D projection when not using facet grids

Details

Adds the following options to the PlotHelper for the z-axis:

• set_labels, including the set_rotate_label option for the z-axis
• set_scales
• set_limits
• set_ticks
• set_tick_locators
• set_tick_formatters

Anything to double-check?

Should be merged before utopya/!17

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated Documentation will be added in utopia/outsource_utopya/improve-plotting-docs

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up
  • Changelog entry added
  • Version number bumped
  • Reviewed & approved by @blsqr @tgaskin

Related issues

Closes #80 (closed)