Add YaCy Search

[davidovski]

Added YaCy search as requested in #204

Removed broken search engines (google and mojeek)

After testing for a week or two, it does have quite a few limitations compared to other search providers:

• results are slow: sometimes taking 10 or more seconds to load the results
• results are innacurate: often times its much harder to get the search result I'm looking for with a simple search compared to duckduckgo or google

Potential improvements:

• add a config option to change which yacy instance's api to use
• switch between yacy instances in a similar way libreX/Y fallback works in case one goes down
• connect to the yacy network itself without having to go through any instance's api (prefered, though it might be beyond the scope of the libreY project)

I believe that the yacy instance hardcoded in this patch is no longer operational, so it might be worth switching it out to a different one (preferably a self hosted one) if you want to test this patch.