Improve `$genericblock` implementation

[ameshkov]

In the current implementation $genericblock is basically the same as $document, i.e. it disables filtering completely.

This implementation can be improved if we change the way the list is ordered.

Here's how the rules should be ordered:

1. Generic css-display-none rules
2. $generichide ignore-previous-rules
3. Generic url blocking rules
4. $genericblock ignore-previous-rules
5. Domain-specific css-display-none rules
6. $elemhide ignore-previous-rules
7. Domain-specific url blocking rules
8. $urlblock ignore-previous-rules

In addition to that $genericblock rules' resource-types should be limited and exclude document. In this case it will not cover cosmetic rules.

Actually, when we add ignore-following-rules support, it will be easier to solve it.