Minor improvements to bot code

[rXn4]

Changed some things that prevented me from having fun in bot matches.
Hope you dont mind that I make quite a lot of pull requests, just have a look at it.

[ruler501]

I think this is good to be merged, I'll see what Victor thinks, then we can merge it.

[theonlypwner]

1. Aiming at the head
   Bots aim at the neck with automatic weapons, which is probably more accurate than aiming at the head (of moving targets). Aiming at the head with sniper rifles makes sense only when they are zoomed though.
2. Lower aim offset for "good" bots
   Is this really necessary though?
3. Less angle offset before shooting
   Just like the comment says, it should really "be skill based", so this change just increases the skill of all bots.
4. Don't reset bots when they run into a wall
   This is a good change, so that they can try doing the stuff in the code below that section (turning and randomly jumping) before being reset.
5. Throttling weapon changes
   Weapon changes are already throttled by m_iChangeWeaponDelay. Adding a global variable to throttle changes is a bad idea because it means that the maximum weapon change frequency is proportional to the number of clients connected to the server divided by the number of bots. Weapon change intervals should be for each individual bot. Having more human players or less bots should not affect how often bots change weapons.