fix(quests): quests with a level cap cannot be bought before that level.

Users were buying the vice quest hoping to play it, not realizing it
would drop at that level. Let's restrict buying the quest (at least in
the short term) until you reach that level.

Fixes #2707.

public/js/controllers/inventoryCtrl.js

@@ -142,6 +142,8 @@ habitrpg.controller("InventoryCtrl", ['$rootScope', '$scope', '$window', 'User',
     }
     $scope.buyQuest = function(quest) {
       var item = Content.quests[quest];
+      if (item.lvl && item.lvl > user.stats.lvl)
+          return alert("You must be level " + item.lvl + ' to buy this quest!');
       var completedPrevious = !item.previous || (User.user.achievements.quests && User.user.achievements.quests[item.previous]);
       if (!completedPrevious)
         return $scope.purchase("quests", item);