added some missing font awesome icons

tracim/models/applications.py

 calendar = Application(
     label='Calendar',
     slug='calendar',
-    fa_icon='calendar-alt',
+    fa_icon='calendar',
     hexcolor='#757575',
     is_active=True,
     config={},
 markdownpluspage = Application(
     label='Markdown Plus Documents',  # TODO - G.M - 24-05-2018 - Check label
     slug='contents/markdownpluspage',
-    fa_icon='file-code',
+    fa_icon='file-code-o',
     hexcolor='#f12d2d',
     is_active=True,
     config={},

tracim/models/workspace_menu_entries.py

   label='Dashboard',
   route='/#/workspaces/{workspace_id}/dashboard',
   hexcolor='#252525',
-  fa_icon="",
+  fa_icon="signal",
 )
 all_content_menu_entry = WorkspaceMenuEntry(
   slug="contents/all",
   label="All Contents",
   route="/#/workspaces/{workspace_id}/contents",
   hexcolor="#fdfdfd",
-  fa_icon="",
+  fa_icon="th",
 )
 
 # TODO - G.M - 08-06-2018 - This is hardcoded default menu entry,