Added property ImplicitMaxTimeStepDivisions and set the default to 10.

Discussed with Bernd, reviewed by Melanie

Dumux-Svn-Revison: 10127
Ported-By: Andreas Lauser <andreas.lauser@iws.uni-stuttgart.de>
CMake: smallish improvements

- we now do not create a 'doc' directory in the install path if
  documentation is not installed.
- introduce a ONLY_COMPILE flag for the EwomsAddTest macro to make the
  2p MPFA test use the same testing infrastucture as everyone else.