boxes/helper: Updated to new quoting style.

[zee-bit]

This PR aims to bring ZT one step more closer to its web counterpart. The quoting style is changed to include the name of the user whose message was quoted(and his user_id) along with a link that would narrow to the quoted message. This is the new markdown/bugdown syntax of a quoted message:

@**Full Name|1234(id)** said[link_to_msg]:
```quote
    quoted_msg
```

For interoperability, the link to the quoted message is the same as that of the web app, so narrowing to the quote in ZT is possible.

Also, the URL generation and encoding part of the code has been shifted to a new module named server_url.py to separate it from the rest of the code inside helper.py and make it easier for constructing and deconstructing server URL in the future.

This PR should fix #514 and #151(partially).

[neiljp]

@zee-bit Initial testing showed this to render fine, though possibly some topics with / in them don't work?

You have the updated quote style ok, but as we discussed in the stream the challenge is how to handle url generation. I'd suggest decoupling the message-to-url part (helper.py is fine for now) as you have done here (from the url-generation part, in another file). The server has url_encoding.py, but it uses other types connected to the server implementation like Realm and it uses f-strings (though we plan to to move to that soon with python3.6). My suggestion would be to use the server file as a basis for a module in our repo which handles chat server urls like this, and we can incorporate your and @preetmishra 's work if it builds upon that in a useful way.

Other than interoperability and tracking changes in the server, the reason I'd like this in a separate file is since we both construct and deconstruct server URLs from narrows and it'd be useful to have it together, and also is related to my hope that we could later integrate this into the python API package.

We can discuss more in the stream if you like.

[zee-bit]

@zulipbot add "PR needs review"

[neiljp]

@zee-bit This is promising, but as per another PR we can tidy this up a little more in terms of commit structure :)

It'll be great to have the bugfix, but as with the other code I'd like to see text of how it was translated across from the server (if it was), and also some tests should help with indicating and checking behavior 👍

[zee-bit]

@zulipbot add "PR needs review"
@zulipbot remove "PR needs update"

[zulipbot]

Heads up @zee-bit, we just merged some commits that conflict with the changes your made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/master branch and resolve your pull request's merge conflicts accordingly.

[neiljp]

@zee-bit I manually merged this just now with slightly adjusted commit text, those extra test cases I mentioned, and squashing the last two commits together. The last commit of the set is 7105240 🎉