Various utilities to use with asQ

[JHopeCollins]

This is a collection of things which we will want to reuse with asQ, but which are not part of the asQ library.

So far this includes:

• units: this avoids silly things like nhours = nseconds*60*6
• mg: this is for multigrid on a manifold sphere, includes factory for the mesh, and the transfer managers
• shallow water: usual forms for linear and non-linear shallow water equations
• williamson: constants and initial conditions for setting up williamson test cases 2 and 5

[JHopeCollins]

Would be nice if there could be a quick test of some of this - maybe just some diagnostics on the initial conditions (total energy, total mass).

Tests now added for:

• values at random samples of williamson2 velocity and elevation profiles
• check that williamson5 profiles match williamson2 profiles
• williamson2 with nonlinear swe gives a reasonably steady solution