Item level content warnings

[singlesoliloquy]

Is your feature request related to a problem? Please describe.
There are no content warnings for material.

Describe the solution you'd like
A clear warning to users that the the content may be graphic or be triggering. Language to be decided.

Additional context
Probably need to be a note and note type. Maybe change the metadata display template to list the content warning first. The display_metadata method might need to be changed or something else done to add a class to that block for styling.