Add ability to copy a content object

[elv-zenia]

Allow user to copy a content object. See associated client-js PR: https://github.com/eluv-io/elv-client-js/pull/128. The content browser modal is identical to the one used by live-manager.

Main test cases:

• Copying an object with no encryption keys
• Copying an object with kms and user caps keys
• Copying an object with one or the other ^
• File download flow for the owner of a copied object
• File download flow for the non-owner (member of an admin group) of a copied object
• Encrypted video files successfully download and play

https://user-images.githubusercontent.com/91760982/141022944-f78c82f0-ac70-4639-bdb7-8e8b7ffb2b39.mov

https://user-images.githubusercontent.com/91760982/141022953-f1bc7718-340a-4943-9561-c5364251ce72.mov

Relates to #8

Future improvements:

• Update sass-lint (disable-next-line is in latest update)
• Update mobx and mobx-react (for the use of makeAutoObservable and makeObservable). Updating these packages broke other pages so I think this should be a separate change to fix any code that needs to be updated.

[elv-zenia]

@elv-kevin Can you review? I think including fields to edit (like name) needs some extra work. Like maybe a multi-step modal. Also, looks like copying to a different library works as well.

[elv-kevin]

one last nitpick before I merge it - hitting cancel on the confirmation shouldn't close the whole thing, just the modal. I think all you need to do is move Close() into the onConfirm function instead of unconditionally after the confirm.