Add Defensive pact (#9900)

* Defensive Pacts can now be offered.

* Signing a defensive pact now makes the Civs join all defensive wars. Any future defensive wars will force the other civ to join.

* Removed Popup Alert Defensive Pact.

* Defensive pact and Research pact now are only on the trade screen.

* AI now offers defensive pacts.

* Added AI evaluating sending and receiving Defensive Pact offers.

* Reverted some temporary changes

* Reduced the chance an AI offers a defensive pact

* Starting an offensive war now cancels all Defensive Pacts with other civilisations.

* Removed extra requirements before an AI will sign or offer a defensive pact.

* Added Defensive Pacts to the Civilopedia.

* Fixed the AI counter offering with treaties.

* Fixed a test using the old method of checking if a civ is at war.

* Fixed a previous refactor error.

* Deleted commented out Research Agreement button code.

* Fixed some spelling errors and remnant debugging code.

* Removed signing a defensive pact brings both Civ's into each others previous defensive wars.

* Refactored setFriendshipBasedModifier to look better

* Starting an offensive war now removes the defensive pact form both sides.

* Reverted changes to DiplomaticStatus

* Removed extra technology check to sign a defensive pact.

* Removed DiplomacyManager.isAtWar() completely.

* Moved setting defensivePact flags from  TradeLogic.transferTrade() to DiplomacyManager.signDefensivePact.

* Changed diplomatic modifiers related to Defensive Pacts to be less extreme.

* Fixed canceling Defensive Pacts when declaring war and notifying other Civs.

* Updated the Defensive Pact entry in the Civilopedia and fixed some spelling.

* Fixed Defensive Pact behavior while attacking and defending.

* Changed a variable to a more readable name.

* Improved readability of setFriendshipBasedModifier().

* Moved the important onWarDeclared functionality to their own functions.

* Added a notification for the attacking Civ when a Civ joins war through a Defensive Pact.

* Refactored setDefensivePactBasedModifier() to be more readable.

* Increased DeclinedDefensivePact time.

* Deleted old commented code that removed the research agreement button.

* Fixed having reverting changes errors in UnitMovementTests.

* Refactored breaking treaties when declaring war.

* Removed unnecessary semicolons.

android/assets/jsons/Civ V - Vanilla/Techs.json

@@ -214,8 +214,9 @@
 				"name": "Chivalry",
 				"row": 5,
 				"prerequisites": ["Civil Service","Currency","Horseback Riding"],
+                "uniques": ["Enables Defensive Pacts"],
 				"quote": "'Whoso pulleth out this sword of this stone and anvil, is rightwise king born of all England.' - Malory"
-			}, // Allows for defensive pacts
+			},
 			{
 				"name": "Machinery",
 				"row": 8,