started on modifying initial conditions

[cekees]

@bchambers28 the critical thing here is to set the initial conditions to be conistent with the soliton set up by WaveTools. Check out the changes I made to ls_p and vos_p--you may need to add the mwl depending on whether eta is relative to the mwl. Then you need to also modify the velocity initial conditions in twp_navier_stokes_p.py. Otherwise you'll just get a falling hump instead of a soliton.

/cc @adimako

[adimako]

This needs to be updated to the two-phase flow format