Ghostery, Disconnect, and uBlock Origin cause requests on first launch

[englehardt]

Support for these extensions was added in #152. All three cause requests to happen on first launch. In particular:

• uBlock Origin requests all of the enabled blocklists
• Ghostery pings telemetry information back to their servers
• Disconnect pings telemetry information and downloads the public suffix list

This is undesirable for two reasons: the lists may change during a measurement, and the downloads are rather large, leading to a lot of unnecessary traffic to the servers hosting the blocklists and the public suffix list. The latter point is particularly a concern for stateless crawls, where the lists will be requested once for every page visit.

I've tried to prevent these downloads by turning off any automatic updating in the extensions, but it doesn't seem to help. I think we'll need to have a priming step, where a fresh browser profile is created and used to launch a browser with the extensions enabled. Once the extensions fetch their remote resources, we can save the profile and use it for all instances of a stateless or stateful crawl. For this to work, we first need to fix #62.

[englehardt]

These extensions are far out of date, and we haven't come up with any general solution to automatically updating them (or the lists they rely on). Instead, we should pull them out of OpenWPM entirely to lower the core platform maintenance cost.

Studies which need to use extensions can add them manually. This ensures that users of the platform grab up-to-date versions.