changed player interpolation

when players start interpolating their past position is set to their
current position and they begin interpolating from their current
position to their new position instead of automatically jumping to the
destination position and interpolating to the new position.
Player position is determined client side

Clients are in charge of updating the server about their own position
instead of having the server update the client's position.

Bug - Clients don't seem to interpolate other players so they jump to
their new position instead of interpolating.