Add new command line args for drivers

* Renormalisation of m after each timestep (default is on for BDF<N>).
* Magnetic parameter sets, default is "simple-llg".
Add "-solver" option to parameter sweep script
When using iterative solvers for LLG switch to a direct solver for large dt

Otherwise we end up huge iteration counts.
Small changes to output

* Output average magnetisations into trace file
* Output headers for dummy variables in trace file
* Some other little stuff...
Use the "good Poisson settings" for poisson preconditioners in semi implicit.