Hotfix: Fix file IO synchronization.

[ghost]

Description:

This fixes File IO synchronization to prevent race conditions for reads/writes, currently towny does something like this:

public void writeFile(File file) {
     synchronized (file) {
          ...
     }
}

This does absolutely nothing because the given file parameter is different whenever another thread uses this method, thus bypassing the locking entirely. This PR fixes this and adds synchronization to other file IO methods.

---

• I have tested this pull request for defects on a server.

By making this pull request, I represent that I have the right to waive copyright and related rights to my contribution, and agree that all copyright and related rights in my contributions are waived, and I acknowledge that the TownyAdvanced organization has the copyright to use and modify my contribution under the Towny License for perpetuity.