Dof ordering for vector/tensor-valued fields

This issue is only relevant for vector/tensor-valued fields

Currently, we are using different orderings for the dofs in different places of the code:

1. `LagrangianDOFBasis` uses "node major" ordering (i.e., first component for all nodes, second component for all nodes, etc.)
2. `CLagrangianFESpace` and `DLagrangianFESpace` use "component major" ordering. (i.e., all components for first node, then all components for second node, etc).
3. `ConformingFESpace`: I am not sure what ordering is being used. To ckeck.

Perhaps it is a good idea to unify things and use the same criterion everywhere.

I would choose "component major" since it is quite standard, and some AMG solvers require that the DOFs are ordered in this way.

I am wandering, why `LagrangianDOFBasis` uses "node major" ordering. Is there any reason?