Inconsistent definition of initial conditions for multilayer tidal shooting method

[jrenaud90]

There is a mismatch in definitions between TS72 Eq. 99 (Takeuchi, H., and M. Saito (1972), Seismic surface waves, Methods Comput. Phys., 11, 217–295.) and KMN15 Eq. B13 (Kamata+ (2015; JGR-P; DOI: 10.1002/2015JE004821)) for the initial guess used in the shooting method for solid layers. TS72 has a "minus/plus" for k2 whereas KMN has a "plus/minus" basically flipping solution 1 and 2.

• Check if this makes a difference to begin with (try flipping solution 1 and solution 2)
• If it does then try to determine which is correct
• Update code and TODOs at:
  • Around line 90 and 314 in tides.multilayer.numerical_int.initial_solution_dynamic.py
  • Around line 90 and 216 in tides.multilayer.numerical_int.initial_solution_static.py

[jrenaud90]

Duplicate of #43