Delete createShallowsPassage / passageMaker from rP11152 and use the unified createPassage function from rP20732 (rP11266, rP12248) to achieve the same shallows generation, refs #4805.

Place shallows at every tributary river rather than leaving out the last 35 percent of the mapsize.
Use vector algebra to do the horizontal/vertical rotation, refs #4845.