Reduce cell model recompiles if only working on functional curation (done for #2428).

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19866 b5f69653-2bf5-0310-8201-b0dafb8e1405
Initial summary info for #2429.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19867 b5f69653-2bf5-0310-8201-b0dafb8e1405
Changes to pycml required for #2428: updates semantics of `input` part of model interface.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19868 b5f69653-2bf5-0310-8201-b0dafb8e1405