#2441 - add method `GetVtkCellDataName()` to `AbstractCellWriter` (plus small edits to `WriteVtkResultsToFile()` code)

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21455 b5f69653-2bf5-0310-8201-b0dafb8e1405
git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21456 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2410 - fix a weekly test, by reducing max dt

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21458 b5f69653-2bf5-0310-8201-b0dafb8e1405
Avoid a Windows compiler warning.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21459 b5f69653-2bf5-0310-8201-b0dafb8e1405