added timing to animate_vorbudget
added bfric calculation for shelf water. also calculating shelfmask separately to make this happen.
Two shelf masks are calculated - one for zrnew axis and one for avg1(zrnew) axis because the vorticity budget terms are on avg1(zrnew) but rv is on zrnew. I need rv to estimate the bottom friction contribution. I'm trying to save time by not interpolating csdye onto both z-axes and then calculating the mask. Instead, I interpolate to zrnew, then avg1 that to avg1(zrnew) - this should not be too different from doing the interpolation.