prisms-center/phaseField: PRISMS-PF (Version 2.1.1)

Minor update to 2.1.1, released in March 2018. The main purpose for the release was to trigger the creation of a Zenodo DOI. A few lingering bugs were fixed. Bug Fixes: Fixed incorrect file extension for the ICs and BCs file in the fickianDiffusion app (Issue #115) Added missing update to a vector containing the past values of integrated postprocessed fields (Issue #120) Other Changes: PRISMS-PF now has a DOI assigned to it (Issue #121) The terminology in the output printed to the screen regarding the linear solver was update