Look into getting default Tor bridges scanned by external reachability tests

[cohosh]

Take to Roya or Paul about tests available for checking the blocking of default bridges.

First determine where development/research is at with Spooky Scan or possibly Censored planet (​https://censoredplanet.org/).

These systems check for blocking remotely and so might tell us something different from OONI.

[phw]

Today, Roya visited as during our weekly anti-censorship team meeting and we briefly touched based on getting reachability scans going. David pointed out that OONI's list of ​default bridges (among other things) would be a great way to get started.

Roya's system has ~50,000 vantage points in 42 "non-free countries" (according to Freedom House's definition) plus a sample of other countries. Roya also wanted to know how often we want these measurements run. "At least once a day" seems like a good answer for now.

For now, I think we should:

1. Get an initial scan going, and see what we can learn from it.
2. Compare the scan results to OONI's data and hope that both systems agree.

[phw]

At ​today's anti-censorship meeting we briefly discussed this project. We decided to move forward with our list of default bridges. These are public and we don't need to worry about sanitising scan results.