AdBlockRule: Add new rule type Invalid for invalid rules
AdBlockManager: Match always by lower case strings
AdBlock: Use fast search tree for basic rules

For all rules that can be matched with simple string-contains match,
use fast tree searching.
Only in EasyList, there is 6000 those rules.
It improves overall performance of AdBlock matching by 5 - 10 times,
at the cost of memory.
The tree needs about 1.5MB memory for 1000 rules, which is a great
tradeoff for such big performance improvement.