new gamemode - keep the base [source included!]

[Alien]

this mode i found in sauer and wolfenstein but with flags - (capture the flag)

Some ideas for this mode or thinking:
1. warning that someone entered or is in your zone
2. warning that you enter to enemy zone
3. if you are in enemy zone, you are getting flag points
4. if you take flag in your zone, all enemies in your zone die and you got -1 flag