Fix #140

1. Injects cookieblocked cookies into disabled pages.
2. Attempts to not delete cookies that user chooses to persist between browser restart if the default is "allow session cookies only". There is no actual way to distinguish these from cookies that PBadger automatically adds to the exceptions list (see #85), so we just assume for now that `userGreen` cookies should be persisted.
3. Adds a bunch of tests.