Linear Shallow Water verification

We now have a set of example programs for the linear shallow water solver that are producing *reasonable* output. It's time to start looking into a more in-depth verification study. This will involve
* Verifying p-refinement convergence rates (varying polynomial degree) in cases where an analytical solution is known ( a new example may be needed )
* Verifying h-refinement convergence rates (varying element size) in cases where an analytical solution is known ( a new example may be needed )
* Verifying time integrator convergence rates
* Assessing the impacts of double and single precision

In working on this issue, I anticipate that recommendations will be developed for improving SELF. Additionally, the verification study *may* find issues in the solver implementation that can be concretely defined so they can be addressed.

**Anyone who wants to tackle this will be given a free account on [Fluid Numerics Galapagos cluster](https://galapagos.fluidnumerics.com/).**