Refactor "author list" dialog

[duartegalvao]

This PR refactors all of the "author list" dialogs, now renamed to "email authors". This dialog is used in abstract, contribution, paper and session lists.

Progress:

• Convert dialog to a React-SUI Modal
• Fetch authors' data
• Display authors' data
• Implement sorting by column
• Allow selecting authors
• Add email button
• Implement filters
• Refactor authors list button implementation
• Show success message in authors list modal
• Use identifiers instead of IDs

[ThiefMaster]

Sorry, but this doesn't work properly yet :/

Sorting doesn't really work either - at least it seems to be case sensitive.

On a much more positive note, the "registered for the event" indicator is now correct while the previous one was incorrect.

I'm also getting some JS warnings:

Warning: Failed prop type: The prop persons[2].identifier is marked as required in PersonList, but its value is undefined.
Warning: Each child in a list should have a unique "key" prop.

PS: I rebased your branch to the latest master and fixed the rebase conflicts (luckily just minor things in Python imports).