Geometric primitives for mesh simplification

[AlePalu]

To implement the mesh simplification algorithm (see, e.g. here) the following primitives should be added:

• check if a line is parallel to the plane spanned by a triangle
• check if a given point belongs to a plane
• check if two segments intersect
• check if a given point is inside a a given element
• compute intersection point between a given segment and a given plane
• check if a point belongs to a line
• query if a point is inside an element, on an edge or coincide with a mesh's node
• query if a point is inside a given mesh or lies on its border