New siege system implemented

All guarded towns now have Town Stones placed and can be sieged

Here is a summary of how the stones and siege works:

• Casting siege on the stone starts the town siege
• After the siege starts, every 10 minutes 1 guard (alive or in the spawnqueue), will be converted into the attacking religions guard.
• During the siege, there will be a global message every 30 minutes warning that the attacking religions hold of the town is growing stronger (just as the beginning and end is announced.
• When all guards have been converted the siege is over and the attacking religion takes the town
• If however, the defending religion casts siege themselves on the stone before all guards have been converted, the siege is broken and all guards are immideately converted back.
• There can be only one siege on-going at same time
• After a succesful siege, you can start another after 48 hours
• If your siege is interrupted, aka failed, you can start another after 48 hours

Starting a siege requires 300 piety.
Ending a siege requires 60 piety.