Ek cleanup

A pack of changes to the EK that cleans up the electrokinetics code for the upcoming release by
(a) removing some deprecated commands (discussed with Georg)
(b) streamlining the description in the UG a little
This time it is independent of the changes to the LB, by basing it on a previous commit (preceding the lattice class):

commit 3261abd662819af1c7df0e0c468374b2bbdc5253