rowindex2rowstart: fix bug and add check

* Add check that row index vector is sorted

* Add insertion of extra row starts up to nrow (requires additional parameter)

* Slightly simplify code
Improve llg_problem get_jacobian as SumOfMatrices for preconditioning

Instead of adding dphib/dphib block into the SumOfMatrices add it directly
into the fem Jacobian. This allows us to solve the fem Jacobian (since it
is now non-singular) and use the solution as a preconditioner for the
complete matrix.
Add option to parse.py to plot n Newton iters
Add preconditioner for SoM which just acts on the main matrix
Modify parse.py to take multiple directory options
Make defauly work properly in view-results.py