Some lib::songtag Refactors

[hasezoey]

This PR refactors some parts in lib::songtag, most notably changing to use async-reqwest instead of blocking, other changes:

• change Service*::search's parameter types to be a enum instead of magic numbers
• add some derives to SongTag (and dependencies) for logging and comparing
• add tests for the to_song_info for each service (except kugou, because of empty response)
• dont serialize and then immediately deserialize the return vectors
• convert static: &str to const: &str

Now there is only 1 usage of reqwest::blocking anymore, that being lib::podcast (and a unreferenced module in playback::rusty::source::http)