Make Coriolis work in all coordinate pairs

[ray-chew]

For now, vertical slices with gravity are in the x-y plane, while horizontal slices with Coriolis are in the x-z plane. Simulations in the x-z plane are solved with a quasi-3D array, i.e. the full grid-size on the x-z plane and in the y-axis, 5 layers of the cellular grid and 6 layers of the nodal grid. These vertical layers comprise the 4 ghost layers.

Making Coriolis simulations work with a truly 2D array will decrease computation time significantly. Two possibilities are:

1. Make it possible for the code to solve x-z plane problems in 2D or
2. extend the x-y plane to support Coriolis.

Option 2. seems to be easier for now, but option 1. will simplify extension to 3D in the future.

[ray-chew]

Consequently, gravity must work in all coordinate directions as well.