HTML filtering rules - void elements are never removed

[ameshkov]

The problem is in the wrong order of checks in ContentFilterRule.

Current implementation:

1. Attributes check
2. Check if content is empty (return NO if empty)
3. Check tag-content and wildcard

Proper implementation:

1. Attributes check
2. Check if tag-content and wildcard are empty. If so - return YES
3. Check if content is empty
4. Check tag-content and wildcard

[vityevato]

CR-AG-710

#20, #25, #26, #29