Newest vertex bisection in 2D [WIP]

[aerappa]

Addresses #709. All tests passing on my machine.

A couple of sticking points that I had:

1. get_cell_node_ids(grid) returns a Gridap custom type Table. It seems this is not intended to be mutable. However, the algorithm I am using requires changing rows for node_ids. For now I a copying this object to a Matrix and doing operations on the matrix. However, I also have another branch where I tried to stick with the table until I got stuck on the mutability. This is probably pretty bad for the memory footprint as well.
2. As I mentioned in the issue, I am sort of "cheating" by not recomputing the labels manually as @fverdugo suggested. Perhaps we can now discuss what he had in mind by this.
3. I only added two files, one in /src and one in /test. I'm not sure exactly what organizational structure is desired.