Improvements for the QR codes

For the hackweek I worked on the bridge QR codes support for Tails.

We have noticed that at the moment multiple bridges (which is the case both of the web request and of the email) are encoded as Python lists. It is almost a JSON format, but it uses single quotes/apostrophes (') instead of double quotes ("). So, parsing the strings is feasible, but not immediate, and I wonder if PT params may include quotes in the future (it would break this workaround).

From the code, I understood that the original intention was having strings separated by \n. This is also compatible with what Tor Browser output (only one bridge line, without any wrapping). Sorry for not checking before. We have still some time to do a last-minute change before Tor Browser 11.5 goes stable.

The Tails's POC implementation can handle both the formats. I don't know if there are other QR code consumers and/or producers, at the moment.

As discussed in IRC, we thought about using the bridge:// URI in the future, too.

Also, I think that PNG would be better as a format, because JPEG doesn't handle sharp edges in a very good way. And we could make them larger, because they are very dense.