WIP: django-learning v1.2 release

Description

This is the Merge Request for the django-learning v1.2b2 release.

Migration and compatibility

• The merge request updates the models, as a consequences, database migrations are needed.
• The merge request breaks the compatibility.
• **CREATE UNIQUE MIGRATION FOR media RENAMED TO attachment.

General TODO

Before being accepted, any merge request must fulfill the following requirements:

• Check PEP8 writing style as described in CONTRIBUTING.md.
• Ensure existing tests are still working properly.
• Features have been tested.
• Every translatable strings are written in proper english.
• Every translatable strings are tagged for translation using gettext, blocktrans and/or trans.
• Ensure that there is no side effect in files: changes are only related to one, and only one feature.
• Ensure that no file has been removed by accident.
• API is documented, as well as the behavior, if needed, in docs.
• Ensure pipeline succeeds.

Release TODO

• Globally update API documentation.
• Globally update external documentation located in docs.
• Update and add (where missing), licence headers and contributions.
• Update the __init__.py version with the appropriate version number: v1.2b2.
• Update the CHANGELOG file.

Current changelog

• Update object sidebar with bookmarks, to distinguish between Course, Activity and Resource, by Nolwenn Machon (@NMachon). See #50 (closed) and #44 (closed).
• Update object colors in order to discriminate between Course #3DB17E, Activity #FBBF44 and Resource #FF4C61, by Nolwenn Machon (@NMachon). See #48 (closed).
• Place holders and help texts were added in forms, by Olivia Bove (@Obove). See #45 (closed).
• The modal window that was used to add or attach an Activity or a Resource has been dropped in favour of two simple buttons, by Raphaël Penault (@PEN.Raph). See #46 (closed).
• The forms were split in multiple tabs, to provide a “process like” functionality when creating Course, Activity or Resource, by Thomas Blot (@tblot). See #49 (closed).