Remove usage of jQuery

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Per previous discussions and especially a couple of comments on bugs, we should move away from using jQuery in conversations.

There's probably several parts to this:

• The gallery view (content/gallery)
• The setup assistant (content/assistant)
• The message pane (content/stub.xhtml & co)

[Standard8]

Note: I'm currently looking into removing jQuery from the assistant.

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#1333 is looking at removing jQuery from the gallery.

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#1345 is the start of the rewrite for stub.xhtml. There's a long way to go, but it has started.

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Status update: a few parts of the conversation view are now based on react - the conversation header and footer, some of the message header, and the attachments display (and a couple of other minor parts). These are getting things working again for 68, though there's a few bugs now.

That's given me enough proof of concept that I'm now working on a larger rewrite of the whole conversation view dropping jquery and replacing the templating mechanism we had there.

I'm not sure the eta for this work - I currently have a few basic items on the messages being displayed, but there's a lot more to do, will post an update or branch when I can.

[Standard8]

I've just pushed the switch of the message list to React onto the master branch. It isn't quite complete yet (I'll file more issues in a moment), but it has now removed jQuery. Hence calling this done.