make it easier to run from different dirs. make it so we can use printf ...

When running CellModeller from an arbitrary location in the file system we need a different way to find the opencl code. This commit assumes that the opencl code is in the same dir as the python code. 

Also if we want to use printf in opencl the %'s in the integrator make it difficult.
I changed the way to add in the reactions so it doesnt use %'s.