Extend weapon functionality

[vurvdev]

1. Events that correspond to https://wiki.facepunch.com/gmod/GM:WeaponEquip and https://wiki.facepunch.com/gmod/GM:PlayerSwitchWeapon
2. Give weapon method
3. Setters for ammo
4. Weapon select method

etc

[Denneisk]

How do you supposed restriction of weapon giving and ammo setters should go? Never mind didn't see a PR was already up for this.

[vurvdev]

Resolved by #2683