Improve Search

[AGulev]

• a way to switch languages for manuals (we don’t support it in current implementation either, so not urgent)
• add videos/courses sections (there is no a separate page per entity in these two, which means the search result should open an external link, which makes implementation a bit harder)
• Maybe some attention to ranking (I spent some time so API headers have higher priority, but maybe something else pops up)
• auto-pick section depends on a page user comes from: if user type something in a search box, API section should be picked