Prevent town deletion, merges and mayor change during occupation

[Angsiyan]

Describe the bug
Towns that are occupied can still delete their town, accept/send merge requests or change mayor, allowing them to easily exit the occupation.

To Reproduce
Steps to reproduce the behavior:

1. Get occupied
2. Run /t delete
3. Town is deleted

Expected behavior
SiegeWar should prevent deletion, merges or changing mayor.

[LlmDl]

SiegeWar expects you to have Town ruining and bankruptcy enabled. Having the town go to ruin prevents the deleted town from re-created in a short amount of time.