List the storybooks where an image is being used

[nya-elimu]

At /content/multimedia/image/edit/<ID>, add a list of storybooks in the sidebar that contain the image in any of its chapters. This will make it easier for content creators to understand if and where the image is being used.

[nya-elimu]

@jacobmass A quick way to test this functionality on localhost would be to go to http://localhost:8080/webapp/content/storybook/list and press the "Upload ePUB file" FAB.

You can find some sample ePUB files here: https://github.com/elimu-ai/webapp/tree/master/src/test/resources/ai/elimu/util/epub