#2517 Get extended bidomain to work with a conductivity modifier (previously it was picking up the intracellular fine through the abstract tissue class, but wasn't paying attention to the modifier in the extracellular or intracellular2 domains).

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21608 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2523 added an exponential distribution to the random number generator

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@21611 b5f69653-2bf5-0310-8201-b0dafb8e1405