Add support for related searches

[jpdillingham]

While investigating #353 it has been discovered that outgoing search requests are accompanied by an additional message with code 153, which informs the server of our search and solicits a list of related searches.

The messages are documented here.

[mathiascode]

SoulseekQt post from 2011: https://www.slsknet.org/news/node/303

I wonder if this feature has been retired though. I tried searching for a bunch of popular artists and music, but no related search terms appeared. Others have also had issues with this: https://www.reddit.com/r/Soulseek/comments/9yddfl/similarsuggestedrecommended_searches/

[jpdillingham]

Thanks for the additional context. After giving it some thought I think this feature is fairly similar to the recommendation (#212) system which also appears to be deprecated.

[jpdillingham]

I've removed this from the roadmap as I believe it to be deprecated (or perhaps just broken) server-side. I'll leave the issue open for now in case anyone wants to investigate further.