Interpolation of ocean height needs updating

[hamishHay]

Currently, ocean height is interpolated to a control volume edge using 0.5*(h1+h2), but this leads to poor performance if control volume edge center does not lie on the line directly between two nodes.

[hamishHay]

Will modify so that ocean height will be interpolated using a barycentric weighting following Eq. 6 in Piexoto (2016). This should be updated in momentumAdvection.cpp as well.