* Add cell image upload modal
* Add controller for serving the images and handle this on markdown side
* Use per-session images dir
* Add etag header to session image responses
* Adjust markdown image styling
* Properly manage session images dir
* Add tests
* Set maximum file size for image uploads
* Move images dir specifics to the Session module
* Move images when nonpersistent session becomes persistent
* Update lib/livebook_web/live/session_live.ex
Co-authored-by: José Valim <jose.valim@dashbit.co>
* Update lib/livebook_web/live/session_live.ex
Co-authored-by: José Valim <jose.valim@dashbit.co>
* Update lib/livebook_web/live/session_live/cell_upload_component.ex
Co-authored-by: José Valim <jose.valim@dashbit.co>
* Test that close gets rid of session temporary dir
Co-authored-by: José Valim <jose.valim@dashbit.co>
