Add a delete content option to the content bank

As an instructional designer
I want to be able to remove existing content from the content bank
So that I can delete wrong or old content

Acceptance criteria:

• Be able to delete existing content.
• The user would see a warning message because we can't know if that content is in use, or where is used. The user could confirm or cancel deletion.

List of tasks:

• Implement needed methods or functions to delete content.
• Implement needed capabilities to delete own/other users' content.
• Implement the warning informing the user.
• Adapt H5P player to be sure there's no error if the file to render doesn't exist.