Added the vlasov8 test case - a more rigourous version of vlasov7

This is similar to vlasov7, but applies a more complex electric field. And so you can visuzalise the results, in the reference branch of the matlab, run

convertFK6DtoRealSpace('path/to/FK6D/output/file/named/fval-MWT.h5')

Running

./fk6d -p 2 -l 6 -d 2 -n 1 -w 1

Should visualize to this ...

with a rel err of 0.029.

Note that I also altered the time at which the applied E field is calculated from simtTime=L*dt to (L-1)*dt, as simTime is the time at the end of the timestep.