Add wasDisplayed to Notification

src/notification-manager.coffee

@@ -48,3 +48,10 @@ class NotificationManager
   ###
 
   getNotifications: -> @notifications
+
+  ###
+  Section: Managing Notifications
+  ###
+
+  clear: ->
+    @notifications = []

src/notification.coffee

@@ -8,10 +8,14 @@ class Notification
     @timestamp = new Date()
     @dismissed = true
     @dismissed = false if @isDismissable()
+    @displayed = false
 
   onDidDismiss: (callback) ->
     @emitter.on 'did-dismiss', callback
 
+  onDidDisplay: (callback) ->
+    @emitter.on 'did-display', callback
+
   getOptions: -> @options
 
   getType: -> @type
@@ -30,12 +34,17 @@ class Notification
   dismiss: ->
     return unless @isDismissable() and not @isDismissed()
     @dismissed = true
-    @emitter.emit 'did-dismiss'
+    @emitter.emit 'did-dismiss', this
 
   isDismissed: -> @dismissed
 
   isDismissable: -> !!@options.dismissable
 
+  wasDisplayed: -> @displayed
+
+  setDisplayed: (@displayed) ->
+    @emitter.emit 'did-display', this
+
   getIcon: ->
     return @options.icon if @options.icon?
     switch @type