Adapt regex to parse new convergence history output

The new KSP monitor produces the convergence history in a different output format. Adapted the regex parser in the visualisation script to account for this.
Control over mass lumping in operator for lowest order elements.

At lowest order the mass matrix in the pressure operator was always set to 'lumped'. Allow control over this setting via the relevant parameter in param_pressure even at lowest order. There was also a bug before since actually param_mixed was used for this setting.
Allow choosing lumped/unlumped velocity mass matrix in lowest order multigrid

Before mass lumping was always used in the lowest order multigrid. This can now be switched on and off to allow more fine grained control.
Merge branch 'allow_no_masslumping_in_multigrid'
Added timers to KSP monitor

To measure the time spent in a KSP solve, I now measure the elapsed time between the __enter__() and __exit__() call in the kip monitor class and print this out in the summary.
Measure time in pressure solve with timed_region

separately also measure the time in the pressure solve with a timed_region construct. The advantage of this is that it gives accumulated timings from which it is easier to infer the average time per iteration.
Use better KSP and PC for velocity mass solve in lumped mass constructor

Instead of using the default, use CG preconditioned with Jacobi, which is fine since the velocity matrix is well conditioned.
Merge branch 'faster_velocity_mass_solve_in_setup'