allow alliance extension Fixes #491 (#1314)

## Description:

About 30s before an alliance is about to expire, both players receive a
prompt to extend the alliance. If both players agree the alliance is
extended.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

resources/lang/en.json

@@ -432,7 +432,12 @@
   },
   "events_display": {
     "retreating": "retreating",
-    "boat": "Boat"
+    "boat": "Boat",
+    "about_to_expire": "Your alliance with {name} is about to expire!",
+    "renew_alliance": "Request to renew",
+    "focus": "Focus",
+    "alliance_renewed": "Your alliance with {name} has been renewed",
+    "ignore": "Ignore"
   },
   "unit_info_modal": {
     "structure_info": "Structure Info",