Uwgeodynamics

- 2D surface processes implementation. Update to surface processes file to include erosion & sedimentation rate or diffusive surface in 2D.
- Tutorials that outline how to use the different surface processes.
- Free Surface examples.

Bug Fixes:
- Drucker Prager Yield Criterion in 3D. A sign error resulted in a lower Yield Stress which resulted in more diffuse weakening when using plasticity with a DP criterion. This has likely impacted all 3D models since early versions of UWGeodynamics. We recommend updating asap.
- Fix some typos in the Rheology references (Asthenospheric type rheology from Watremez et al was referred as Lithospheric)
- Fix Free surface implementation.

- Change Passive Tracers Interface. The ``Model.add_passive_tracers`` method now return ``None``. Tracers can be accessed via the Model object. This is to avoid orphans and usage errors when doing a restart.
- Add option to pass UW function (or mesh variable) to the density material properties.
- `Model.init_model()` excepts arguments to optional to initiliase temperature and pressure fields with an UW function or a mesh variable.
- Various bug fixes.

- Layer2D which has now been deprecated for a while has been removed

User related changes:
- The 'visualisation' python module replaces the 'glucifer' python module (as per UW 2.9)
To update in your model, replace the line
`import glucifer`
with
`from UWGeodynamics import visualisation as vis`
'vis' can be used as 'glucifer' was.

- Compatible with UW 2.9
- New Numpy Pressure Smoother

Enhancements:
- Upgrade to Dockerfile configuration, using "muli-stage" builds.

Bug Fixes:
- Passive tracer initialisation in 3D.
- Restarting with track fields and swarm global indices.
- Passive tracer interface changes. vertices must be passed as a numpy array