Add support for drop down menu in the navigation bar. Simplify the home screen.

mayan/apps/documents/menus.py

@@ -0,0 +1,9 @@
+from __future__ import absolute_import, unicode_literals
+
+from django.utils.translation import ugettext_lazy as _
+
+from navigation import Menu
+
+menu_documents = Menu(
+    icon='fa fa-file', label=_('Documents'), name='documents menu'
+)