CONNT-25: Updated change_list.html admin template:

- Enclose the object-tools-items block content with a permission
check, same as in current version of Django Admin (1.11.x).
- URL generation has _not_ been brought up to date.

CONNT-25: Updating application and project to use Django 1.11.x:

- Bumped Django version in both the development requirements and setup
script to 1.11.x.
- Bumped Django Crispy Forms to version 1.7.0 in both development
requirements and setup script.
- Updated import of URL-related modules to use the new path (previous
one is deprecated).
- Added explicit on_delete = models.CASCADE option to all foreign key
fields (old implicit behaviour will be deprecated in Django 2.0).
- Fixed the custom change_list.html template used in Django Admin to
render without errors.