Try narrower cells on dayside for better ulf propagation

[iljah]

Solar wind carries/induces ultra low frequency waves in magnetosphere, try simulating 3d test with cells that are e.g. 2-8x narrower towards sun before adaptive mesh refinement with https://github.com/fmihpc/dccrg/blob/master/dccrg_stretched_cartesian_geometry.hpp
This should increase frequencies that can get from solar wind boundary to magnetosphere with e.g. 4-64x fewer cells on dayside than with cubic cells.

[iljah]

Requires #23