#2364 (hopefully) fix leaky halo data in cell-based. And some whitespace :)

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18802 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2380 - attempt to fix memory leak

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18805 b5f69653-2bf5-0310-8201-b0dafb8e1405
#1902 give a bit more access to some member of `NodesOnlyMesh` to subclasses so we can set up parallel SEM simulations more efficiently

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18818 b5f69653-2bf5-0310-8201-b0dafb8e1405