Delete static page (HHU #427)

allows deletion of static pages (fixes HHU #427)

it creates a new link to the edit static pages html, this link generates a confirmation html (ask_delete)
which deletes a specific static page from database

changed files:
#2 routing rules added for ask_delete and delete 
../config/routing.py     2 routing rules added for ask_delete and delete 
#new template (general adhocracy no theme) for delete confirmation
../templates/static/ask_delete.html
#added delete link to edit template
../templates/static/edit.html
#2 new function in static controller ask_delete and delete
../controllers/static.py
#new function to delete static page in database
../model/staticpage.py