Split up solver and preconditioner command line args
Use CG and amg w/ poisson settings by default for poisson problems
python 3 compatability in parameter-sweep.py
Use python loop rather then find+xargs when compressing results

More reliable, easier to read + debug.

Also some new parameter sets.
Improvements to output format and parse script

* Tidy up data printing code
  seperator first: cleaner python code
  properly write all headers

* Update parse script to work with this

* Lots of other stuff in parse, don't know what really...
Changes to problem classes

* Add superlu default solver (the one in Problem is private so hard to use)
* Initialise meshes in block preconditioners during build()
Unify smoothly_varying_** initial magnetisation functions
Limit iterative solvers to 200 iterations before failing
Add factory for creating llg block preconditioners

(early work still...)
Move midpoint method to oomph-lib/src/generic folder

* Including tests