Add Custom Assembler with Nodal Tensor Product Element

[IgorBaratta]

• Scalar Mass Matrix on Quads
• Scalar Mass Matrix on Hexes
• Vector Mass Matrix on Hexes
• Scalar Stiffness Matrix on Quads
• Scalar Stiffness Matrix on Hexes
• Vector Stiffness Matrix on Hexes

Tensor product Gauss-Legendre (GL) with q=p+2, p is the polynomial order of the element.
Use nodal basis with p+1 Gauss-Legendre-Lobatto (GLL) points in each spatial dimension.