Theoretical comment.

- denote other possible transformation of isotherms
- remove development notes from sorption.hh
First steps to working test 09

- fix OutputTime::mark_output_times
- virtual output_data method in EquationBase
- remove direct call of DarcyFlowMHOutput from hc_explicit coupling
- DarcyFlowMHOutput created internally by DarcyFlowMH classes
- fix TimeMarks::is_current to work for variable staedy time governors
- remove default parameter from FieldCommonBase::set_time
- reorganize DarcyFlowMH constructors; remove unnecessary data members
Add test 09 to CI

- add test 09
- try to fix cleaning of the workspace