curvilinear bits 'n pieces - #538

New stuff includes:
- Variable vector dirichlet boundary conditions,
 `CurvilinearDirichletCondition`, driven by uw.fn.
- A system wide rotation matrix that can be used for stokes or rotating a vector mesh variable
- Meshes with non cartesian geometries.
New examples under, docs/examples/curvi_examples.

...ode/underworld2 into jgiordani/curvi-bits

* Fix issue 537 - vrms typo
* Making sure the factor is an appropriate numpy type
* Updates for docker image generation: (#550)
* Switch deprecated `MAINTAINER` tag for new `LABEL` construct.
* Set `/opt` to ugo+rwx to allow users to install new pip packages.
* Remove `tini` which no longer appears to be required (and wasn't
 being used previously in any case).
* Remove extras for notebook MPI usage, as this wasn't being used
 and is easy to reinstall.
* Update UW image to point to newest base file image.
* Update to CHANGES.md
* Renaming guidelines.md -> development_guidelines.md
* * Fixes h5 file save mode (underworldcode/underworld2/#533)
* Minor documentation updates.
* Minor redundant code removal.
* Adding a pull request template!
* Update `CHANGES.md`
* Update to fix broken ReadTheDocs generation.
* * Import scaling into uw. (#554)
* Fix docstrings & doctests.
* Rename pull request template as Github doesn't appear
 to register it with upper case naming.
* Fix test in config which Py3.8 is complaining about.
* * Added a check to ensure that the selected solver is available at runtime. (#553)
The previous behaviour resulted in solves continuing unaware of solve
 difficulties, and failing elsewhere, or worse.
* Added test for the solver check.
* Solver check (#555)
* * Added a check to ensure that the selected solver is available at runtime.
 The previous behaviour resulted in solves continuing unaware of solve
 difficulties, and failing elsewhere, or worse.
* Added test for the solver check.
* I've updated these models to run with "mumps" if available,
and fallback to the default solver otherwise.
* Using a relative path to reload swarm files
* * For sequential IO operations, need to ensure that
 non-root procs open file with `append` mode instead
 of `write` mode (otherwise a new file is created by
 each proc, effectively deleting all data previously
 written).
* Update mesh file mode to `write` mode.
* Making test_long.sh executable
* Adding a EBA example to the tests for now. Documentation will come next
release when it's moved into examples.
The 2 extra terms in the heat equation, viscous dissipation and
adiabatic heating, should have equal volume integrals in the model, as
per King et al.
* Update CHANGES
* github actions docker images
* * Documentation, version numbers, and docker file updates. (#559)
* File creation mode should be "w" here too. Interesting, "append"
 mode causes a test failure in the Docker container, but not baremetal
 Ubuntu.
* Update docker_build_push.yml
* Update docker_build_push.yml
* Update docker_build_push.yml
* Adding symlink to `LICENSE.md` for conda.
Co-authored-by: John Mansour <mansourjohn@gmail.com>