MeshDataContainer operator[] for integer sequence
JSONLogger accepts references instead of values

fix hexahedron reader

add makeBoundaryIndex

methods isInvalidIndex, isBoundaryIndex, extractBoundaryIndex

the class MultiphaseFlow is now a template

parameter dimension.

necessary to transform the gradient into standart bases anymore. Also
generalized some Vector(Vertex) operations to be applicable to second
order tenzor as Vector<Vector>.

Debug singleton
Vertex multiplying from both sides
the computation works with Traits

fix of operator- for traited classes

differs.