Define the groups on the model of blocks

A group is characterized by the three following components:

• its type

• its name

• its elements

The six following classes define all the kind of group:

• group3d for groups of hexahedra,

• group2d for groups of facets,

• group1d for groups of segments,

• group0dVertices for groups of nodes on the edges,

• group0dFaces for groups of of nodes on the faces,

• group0dBlocks for groups of nodes in the blocks,

See TUI scripts and GUI part.