Simplify logic of Menu::alliance
Simplify logic of Menu::alliance

* Merge hidden player check into the `$in_alliance` variable, to avoid
  repeating the check for every menu item.

* Make the treaty permission variables available even if in the
  alliance. While this was not an error, it did cause unneccessary
  Scrutinizer warnings, e.g.

> The variable $modRead does not seem to be defined for all execution
> paths leading up to this point.

hemberger/smr,smrealms/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr