[abp2blocklist] Add unittests

[sebastian]

Background

With #3671, abp2blocklist provides a proper API. So we can finally start writing automated tests. We want to use ​Nodeunit as that is what we use for the adblockpluscore repository.

What to change

Introduce unittests, that run against the API introduced with #3671. The tests should be as granular as possible, and include at least following test cases:

• Verify the order of generated blocking rules, regardless of the order in which the corresponding filters been passed to the API. The mandatory order is:
  1. Element hiding rules
  2. $elemhide exception rules
  3. Request blocking filters
  4. Other exception rules
• Verify that Adblock Plus request type filter options are mapped correctly to the corresponding trigger.resource-type.
• Verify that unsupported filter, like those using the $sitekey option, are ignored.
• Verify that other filter options, including $domain, $third-party and $match_case, are converted correctly.
• Verify that IDN domains are converted to punycode.
• Verify that filters that use non-ASCI characters (that aren't converted as part of the domain) are removed from the resulting block list.
• Verify that element hiding exceptions cause the respective element hiding filter to be removed from the generated block list.
• Verify that ID selectors are replaced wit attribute selectors, see #3584.

[abpbot]

A commit referencing this issue has landed:
​Issue 3675 - Test ContentBlockerList