Merge pull request #18 from HaibingShao/react_trans_GIA

React trans gia
implementing activity model, second version; using activity directly in LMA.this is not converging.
Merge branch 'react_trans_GIA' of github.com:zolfagha/ogs into react_trans_GIA
Merge pull request #59 from zolfagha/react_trans_GIA

Using activities instead of concentrations and constant K values.