Smooth movement

Makes NPCs and player movement smoother. Resolves #5610 (closed) and #4894 (closed).

Motivation: for some people jerky movement causes motion sickness. This change makes the movement and turning not so sharp.

To enable add to settings.cfg:

[Game]
smooth movement = true
NPCs avoid collisions = true
turn to movement direction = true  # recommended because NPCs will use diagonal movement

Changes:

1. NPCs move and turn much more smoothly.
2. NPCs avoid collisions when move (resolves #4894 (closed)).
3. Standing NPCs give way for moving ones if they are not busy with something important (Have you ever been blocked in a narrow passage by your own follower? It shouldn't be a problem any more). Can be disabled by setting NPCs give way to false in [Game] section of settings.cfg.
4. Turning in combat is slower and not jerky now. NPCs do a side step if someone tries to go around, so backstabbing is not easier than before.
5. Head tracking works in combat.
6. Transition from standing to moving is not instant both for NPCs and for player.
7. Player turning is also not instant. Try turn very fast while running and you will see the effect of "turn to movement direction".

Examples

NPCs movement

• Before: https://streamable.com/wc3ola
• After: https://streamable.com/yd0d2b

Combat, single enemy

• Before: https://streamable.com/bu8hb7
• After: https://streamable.com/xh2kxp

Combat, many enemies

• Before: https://streamable.com/7rlxzb
• After: https://streamable.com/zsqjy0

Avoiding collisions

• https://streamable.com/fj591z

Looking forward for feedback.