CIDEVMI-1105: WAVSS DPA functions and tests - initial code

DPA code makes assumptions that need to be coordinated with dataset agents, and is
therefore not ready for optimization.

Uses vectorized magnetic corrections function copied from adcp_functions; consider incorporating 
this vectorized version into generic_functions module.

Changed rtol parameter from 1e4 to 1e-4 in test_magnetic_correction function in test_generic_functions 
module; extended number of significant  figures for the affected test values. Note, the magnetic_correction 
function in generic_functions was not used in the WAVSS DPA code. 

@s-pearce Ready for review and merge.
@cwingard Ready for review and merge.