Create unambiguous timeline paper element

app/assets/javascripts/angular/timelines/models/mixins/ui.js

@@ -296,7 +296,7 @@ angular.module('openproject.timelines.models')
     },
     registerDrawPaper: function() {
       // store the paper element for later use.
-      this.paperElement = jQuery('.tl-chart')[0];
+      this.paperElement = jQuery('#timeline-container-' + this.id + ' .tl-chart')[0];
     },
     getMeasuredHeight: function() {
       return this.getUiRoot().find('.tl-left-main').height();

app/assets/javascripts/angular/timelines/models/timeline.js

@@ -58,11 +58,13 @@ angular.module('openproject.timelines.models')
   //startup
   angular.extend(Timeline, {
     instances: [],
-    create: function(options) {
+    create: function(id, options) {
+      if (!id) {
+        throw new Error('No timelines id given');
+      }
       if (!options) {
         throw new Error('No configuration options given');
       }
-      this.options = options;
       this.extendOptions();
 
       this.instances = [];
@@ -70,6 +72,8 @@ angular.module('openproject.timelines.models')
       var timeline = Object.create(Timeline);
 
       // some private fields.
+      timeline.id = id;
+      timeline.options = options;
       timeline.listeners = [];
       timeline.data = {};
 
@@ -723,7 +727,5 @@ angular.module('openproject.timelines.models')
     };
   }
 
-
-
   return Timeline;
 }]);