Documentation improvements before release

[janvonrickenbach]

• Finish getting started

  • Add documentation on how to run local server from installer

• Rename Objects and Helpers

  • Use different subgroups or use more descriptive name.

• pyDPF Composite shows up twice in the header because the developer's guide is named like that.

• Mention operator type in get_dpf_material_id_by_analyis_ply_map

• Mention operator return type in add_layup_info_to_mesh and better document composite_definition_label. Mention that layup operator is returned.

• get_constant_property: Mention how materials provider operator can be obtained.

• Mention corresponding example in API docs of Material Properties.

• CompositeModel: Replace self by class name. Mention assembly example in docstring. Document arguments of init properly.

• Show enum values in docs (spots...)

• Make sure available material properties are shown in docs

• Document ContinuousFiberCompositeFiles.composite

• In LayupPropertiesProvider: Mention how layup_provider can be obtained.

• API docs: Think about order. Make it alphabetical or move most important items to the top.

• Sort the examples by increasing complexity

• Examples: Replace get_combined_failiure_criterion function by variable assignment.

• Go through examples and fix minor typos and wrong cell labels.

• Don't use strings to instanciate dpf core operators

Optional:

• Check links to matplotlib documentation
• Remove ansys.dpf.composites prefix for class names
• Create documentation for operators and link them in API docs #147
• Fix developers guide and mention that dpf containers are not publicly available. Document how to run unit tests with dpf server from unified installer.