Small changes to check health method in Tools.
Added modes to BC setup.

The modes are working similar to geometry module.
Minor changes to Fickian diffusion.

These are just some small changes behind the scene to make the algorithm
work with the new BC setup.
Minor adjustments to the algorithms.

To make the rest of the algorithm modules  consistent with the Fickian
algorithm and also new setup for boundary conditions.
Removed the old version of BC setup.
Removed default occupancies in Generic Fluid.