Draft: Django 2.0 Upgrade

This MR intends to upgrade Django to version 2.0 2.2 (thereafter referred to by just 2.0)

The following things are changed:

• Bumped some dependencies' versions (Django itself and some CMS Plugins)
• Imports/methods that were removed in 2.0 have been removed
• Added required args/kwargs for ForeignKey and OneToOneField introduced in 2.0 (Both in Application code and in Migrations)
• Changed URL include to use new style in URLConfs
• Changed Middlewares to use new style

Edit :2.0 has some issues with migrations that seem to be fixed 2.1 onwards. So, the goal now is to upgrade to 2.2