Actualize Low-level settings article

[ameshkov]

Currently, we have a bit outdated article: https://adguard.com/kb/adguard-for-android/solving-problems/low-level-settings/

Here's what I suggest:

1. Move the article to the "Features" section (it's more a feature than a solving problems content).
2. Actualize the article (for starters, information about dev tools that we added in v4.3 is missing: https://adguard.com/en/blog/adguard-v4-3-for-android.html)