MeshData representing vectors

[bmxam]

Currently, MeshData only accept an AbstractVector (by opposition with AbstractMatrix). When we want to represent a vector field, should we:

1. modify the implementation of MeshData to accept matrices, then the "get_value" will look like get_value(data,i) = view(data,i,:)
2. build a MeshData with a "vector of vectors" : MeshData([[u1_x, u1_y], [u2_x, u2_y], ...])

?

For sure method 2. does the job for now, but I am just asking the question. Note however that, with solution 2, our write_vtk methods will fail for MeshCellData (because we don't materialize them, we just get the values).