translate abstract methods to new API

weboob/backends/youporn/pages/base.py

@@ -22,7 +22,7 @@ import ClientForm
 from weboob.tools.browser import BasePage
 
 class PornPage(BasePage):
-    def loaded(self):
+    def on_loaded(self):
         try:
             self.browser.select_form(nr=0)
             self.browser.submit(name='user_choice')

weboob/backends/youporn/pages/video.py

@@ -28,7 +28,7 @@ from weboob.capabilities.video import Video
 class VideoPage(PornPage):
     URL_REGEXP = re.compile("https?://[w\.]*youporn.com/watch/(\d+)/?.*")
 
-    def loaded(self):
+    def on_loaded(self):
         if not PornPage.loaded(self):
             return