docs: add debugging section to installation.rst
report no entities error in Region.setup_from_highest()
fix default in Config.tetgen_path()
use region space dimension instead of field shape in vector LCBC operators
use DOF per node count instead of field shape in IntegralMeanValueOperator
update Field.from_args(), __init__() docstrings (shape parameter)
update Field: new n_components, val_shape attributes, new H1Mixin

- new H1Mixin._setup_shape(), update Field.__init__()
- update Field docstring
inherit H1NodalMixin from H1Mixin, update .set_dofs()
inherit H1HierarchicVolumeField from H1Mixin, update .set_dofs()
remove n_components argument in Variable, FieldVariable constructors

- update Variable.__init__(), FieldVariable.__init__()
- update Variable._setup_dofs() - new n_components, val_shape arguments
- update FieldVariable._set_field() - set n_components, val_shape from field
update sfepy.fem modules for no n_components argument
update scripts, examples and tests for no n_components argument
docs: update for no n_components argument
remove Field.setup_dof_conns() (duplicated in VolumeField.setup_dof_conns())
remove dpn argument of {VolumeField, SurfaceField}.setup_dof_conns()

- update setup_dof_conns()
update active DOF connectivities only when needed in Equations.time_update()

- initialize adof_conns in Variables.__init__()
remove unused filename argument of IntegralMeanValueOperator.__init__()

- update LCBCOperators.add_from_bc()
save LCBC data only in the initial time step of LCBC application

- update FieldVariable.create_lcbc_operators()
- partially addresses #215
remove active argument of FieldVariable.get_dof_conn()

- update Term.assemble_to()
update Variable.get_primary(), .get_dual() for incomplete variables