Added experiment comparing with analytical results for spatially constant case

Analytical formulae for time and phi as functions of theta and initial
theta taken from Mallinson2000. No exchange field can be included but
others are used.

Also added various scripts to generate and deal with the data.

Added some functions for manipulating the magnetisation from oomph-lib to
b/implicit_llg_problem.h.

Added some general functions for manipulating vectors to vector_helpers.h.