Add capture-window variable to battle points

[cicetil]

Currently, battle points have a cooldown timer but not a time limit for capturing a point. As a result of this, the team which currently holds a point will have to defend it indefinitely until it inevitably gets captured by another team.

To give defending teams a reason to fight over a point they control, there should be a - capture-window option which is a timer in which the battleground is able to be captured after it becomes available.
ie. if capture-window=30m when the battle point becomes available, players will only have 30 minutes to capture it. If it is not captured within time, it stays under the current team's control. If no team currently controls it, it will stay uncontrolled until it becomes available again.

When the currently controlling team successfully defends a point, any members of that team that are within the battleground will receive rewards as though they just captured the point.