Further improvements of "view over shoulder"

Follow up to !219 (merged) "Improved third person experience". Related issue: #390 (closed).

Changes:

1. If player starts swimming, camera slowly moves from "over shoulder" to "above head" position.
2. New feature "auto switch shoulder". If player goes close to a wall, then camera automatically switches to the shoulder that is farther from the wall. Can be disabled with "auto switch shoulder = false".
3. Camera moves slightly away from the character when the character runs.

See forum thread for illustration to 1. Small video to demonstrate "auto switch shoulder": https://streamable.com/d4l100

All the changes makes difference only in "view over shoulder" mode:

[Camera]
view over shoulder = true