Shifted nametags to separate script

NameTags.pwn now contains nametag toggle function.
Tags are toggled on when an admin goes on spectate mode, not when they
go on duty to minimise the possibility for abuse (abuse can be checked
using the standard /spec usage checks). Tags are then disabled when the
admin goes off duty (not when they exit spec)

Also added a level 4 command for toggling nametags at any time (even
when not on duty). Can be heavily abused so beware who is level 4.
Optimisation for IsPlayerInWater from Kar2k

Thanks @Kar2k!
Removed redundant check that caused a bug

This check stopped character saving if the character quit/logged out
while dead and under some other conditions (currently uncertain,
involved the pause menu and some other factors)

This appears to fix the issue but may not yet, still needs thorough
testing on a public server.