Support bulk delete of user media

[AverageMarcus]

Fixes #121

• Adds multi-select to the user media list to allow for bulk deleting media.
• For image types, a preview is also displayed in the list

Example:

Note: I've never used React before so not sure if the way I've implemented everything is the most ideal or not, would love any feedback.

[AverageMarcus]

Thanks for the great feedback @dklimpel ! Hopefully addressed everything now.

[WebFreak001]

I think the preview could be a violation of GDPR, right? Looking at private content uploaded by users e.g. in a private chat without their consent would be a violation unless the server's privacy policy explicitly says admins may look at for some given reasons.

[awesome-michael]

Thats a good point @WebFreak001. I think the preview should not be displayed by default. Maybe there is a scenario where admins have to look into the images (e.g. when they were reported) but I also think that the users have to be aware that this is possible. Maybe the server should allow admins to read the images then. Would the preview even be available for pictures that were uploaded to encrypted rooms?

[dklimpel]

Encrypted images does not match record.media_type.startsWith("image"). An admin can not read encrypted images.

e.g.

[jank04]

Any Update on that? Is there a possibility to shift + leftclick, so that you can select multiple tick-boxes at once?

[dklimpel]

Perhaps this could be in feature replaced by BulkUpdateFormButton.

[awesome-manuel]

I think bulk delete is already available in the latest master. If this is only about image previews, please rename the PR.