feat : Split "Add a new Activity/Resource" button into seperate buttons

Description

Adding a new feature,split the first button into the other two will allow us to enhance the user experience by reducing the number of click needed to add an activity to a course or to add a resource to an activity.(ref : #46 (closed) )

Migration and compatibility

• The merge request updates the models, as a consequences, database migrations are needed.
• The merge request breaks the compatibility.

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 the commit history is “clean enough” (this means no extra merge commits, etc).
• Ensure pipeline succeeds.

Impacted Areas in Application

Details of courses and activities, add an activity/ressource