[Cleanup] Rename: VelocityUpdater -> RateUpdater

src/CMakeLists.txt

src/adaptivetimestepper.hh

src/coupledtimestepper.cc

src/coupledtimestepper.hh

src/coupledtimestepper_tmpl.cc

src/fixedpointiterator.cc

src/fixedpointiterator.hh

src/fixedpointiterator_tmpl.cc

src/rate.cc

src/rate.hh

src/rate/backward_euler.cc

src/rate/backward_euler.hh

src/rate/newmark.cc

src/rate/newmark.hh

src/rate/rateupdater.cc

src/rate/rateupdater.hh

src/rate/rateupdater_tmpl.cc

src/rate_tmpl.cc

src/sand-wedge.cc