Further extend content control

[Helium314]

The recent update greatly increases compatibility with AdGuard and uBlock origin extensions of the AdBlock Plus filter syntax.
But still there is some work left:

Differences between ABP / AdGuard / uBO:

• important: works on exception rules and blocking rules, as it does in AdGuard. In uBlock origin, important works only when used as a blocking rule.
• host names: are interpreted like in uBO
• document: behaves like in uBO
• strict blocking: behaves like in uBO
• contrary to uBO, filters like in this issue work

Not fully implemented:

• modifier filters may break some websites, even if requests are not modified at all. This is due to some problems when using okhttp to do requests for WebView.
• badfilter does not work if $domains of badfilter and original filter is different, does not work on * and similar filters with domains
• all might not be implemented correctly

Unsupported, planned to implement:

• cookie
• rewrite
• webrtc
• header: still experimental in uBO
• ping: not sure if this is applicable to WebView
• network: not sure if this is applicable to WebView
• cname: not sure if this is applicable to WebView
• pre-parsing directives

Unsupported, low priority:

• element hiding / cosmetic filtering
• html and js rules
• replace

Unsupported filters, no plan to implement:

• genericblock
• content
• jsinject
• urlblock
• extension
• stealth
• app
• popup / popunder: no popups / popunders in WebView to my knowledge
• object, object-subrequest: no such plugins in WebView to my knowledge

This issue serves as an overview to see what needs to be improved.