Pull customizations to the Disconnect list into another file

[fmarier]

We have a few webcompat-related customizations in our fork of the Disconnect list.

It would be good to pull these out into a separate file so that we can then pull directly from the upstream disconnect list or alternatively the Firefox fork of it.

[fmarier]

Reopening since #37 re-added a customization.

[fmarier]

One way to do this would be to move our customizations to a separate file and then write a script that would:

1. Pull down the latest https://github.com/mozilla-services/shavar-prod-lists/blob/master/disconnect-blacklist.json into a temporary json file.
2. Automatically add our extra entries to the temporary json file.
3. Run json_verify over the temporary json file.
4. Rename the temporary file to disconnect.json.
5. Build the extension and generate the TrackingProtection.dat file.