- added Polygon specialization for EntitySeed and EntitySeedHash that uses Array instead of StaticArray to handle variable number of cornerIds
- refactored template argument EntityDimensionTag of SubentitySeedsCreator to EntityTopology to allow specializing for Polygons
- added Polygon specialization for SubentitySeedsCreator to handle variable amounts of vertices per polygon
- added getSubentitiesCount function to SubentitySeedsCreator to retrieve number of subentities to be created from passed in vertices
- modified Initializer::initSubentityMatrix function to retrieve capacities from a method argument instead of creating them statically from traits and to pass in retrieved capacities to Mesh::setSubentitiesCounts
- removed EntityInitializer::initSubvertexMatrix function and replaced all calls to it with Initializer::initSubentityMatrix
- modified EntityInitializerLayer::initSuperentities and InitializerLayer::initEntities functions to calculate subentity matrix capacities before a call to Initializer::initSubentityMatrix

- added SubentityMatrixType to MeshSubentityTraits and modified SubentityMatrixType in MeshTraits to get SubentityMatrixType from MeshSubentityTraits based on Dimension and Subdimension template arguments
- refactored template argument EntityTopologyDimensionTag of SubentityStorageLayer back to EntityTopology to allow specializing for Polygon
- added Polygon specialization for MeshSubentityTraits that uses different SubentityMatrixType and leaves out any count related defined types
- added Polygon specialization for SubentityStorageLayer, that unlike SubentityStorageLayer used in other cell topologies, additionaly stores subentiesCounts
- added setSubentitiesCounts function to mesh and its storage related parent classes for setting subentitiesCounts in SubentityStorageLayer
- modified getSubentitiesCount function in mesh to pass the unused entityIndex parameter to StorageBaseType::getSubentitiesCount to enable retrieving variable subentitiesCounts from Polygon specialization...

- added Polygon to Topologies
- added mapping of Topologies::Polygon to EntityShape::Polygon in VTKTraits
- added a missing reference to a variable in MeshBuilder::validate

mesh refactoring: moved points from StorageLayerFamily to Mesh, replaced template argument EntityTopology of SubentityStorageLayerFamily and SuperentityStorageLayerFamily by DimensionTag

Move-constructors with a 'const' argument do not make sense. And the
ChunkedEllpack and SlicedEllpack implementations did not even use
std::move!

Documentation for linear solvers and preconditioners

See merge request !116

Iterative solver monitor does not print elpased time, time and tau if one does not set timer and time step respectively.