Merge remote-tracking branch 'origin/master' into 43-add-support-of-continua-with-variable-number-of-degrees-of-freedom

Resolve "Moving a Mesh invalidates iterators in Assembler"

Closes #48

See merge request mechanics-and-materials/ae108!54

Resolve "Build image via Docker Compose"

Closes #68

See merge request mechanics-and-materials/ae108!60

- (re-)building Dockerfile simplifies modifications

Resolve "Add function to explicitly compute the Schur complement"

Closes #65

See merge request mechanics-and-materials/ae108!58

- computes the elements of a matrix created by asSchurComplement

Resolve "Run examples in CI"

Closes #36

See merge request mechanics-and-materials/ae108!55

- fixes error in CI

- json files do not support comments in file header
- stdout.txt contains output of test
- fixes error in CI

- fixes error in CI

- uses definition.json files in tests/*/* to detect test configurations
- add configurations for examples: Basic, CuboidMesh

- fixes error in CI

- fixes error in CI

- IteratorRange no longer used
- IndexBasedAccessIterator no longer used

- views use SharedEntity instead of Mesh
- Mesh can be moved without affecting views

- manages PETSc's reference counting

- LocalEntityIterator no longer required

Resolve "Add `Context` to manage initialization/finalization"

Closes #63

See merge request mechanics-and-materials/ae108!56

- fixes error in CI

- additional scope is no longer needed

- automatically calls PetscFinalize on destruction

Resolve "Add example that uses ForceElement"

Closes #31

See merge request mechanics-and-materials/ae108!53

- useful for testing output with larger datasets

- permits multiple types of elements
- adapt generate_xdmf for modified output

- cpppetsc's HDF5 output does not support multiple types of elements