Team UI with max teams slots

www/common/common-constants.js

@@ -16,6 +16,7 @@ define(function () {
         tokenKey: 'loginToken',
         displayPadCreationScreen: 'displayPadCreationScreen',
         deprecatedKey: 'deprecated',
+        MAX_TEAMS_SLOTS: 3,
         // Sub
         plan: 'CryptPad_plan',
         // Apps

www/common/common-ui-elements.js

@@ -3746,8 +3746,15 @@ define([
                 console.log(err);
             });
         };
+
+        var MAX_TEAMS_SLOTS = Constants.MAX_TEAMS_SLOTS;
         var todo = function (yes) {
+            var priv = common.getMetadataMgr().getPrivateData();
+            var numberOfTeams = Object.keys(priv.teams || {}).length;
             if (yes) {
+                if (numberOfTeams >= MAX_TEAMS_SLOTS) {
+                    return void UI.alert(Messages._getKey('team_maxTeams', [MAX_TEAMS_SLOTS]));
+                }
                 // ACCEPT
                 module.execCommand('JOIN_TEAM', {
                     team: msg.content.team