#2260 fix nightly builds. Enable `NodeBasedCellPopulation` to use the load balance algorithm. Switch off by default.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19199 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2260 typo

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19200 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2260 enable load-balance to happen at intervals rather than every time-step.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@19201 b5f69653-2bf5-0310-8201-b0dafb8e1405