Add/Remove songs to My Music.
Fix segfault because of adding song to library.
Cashing settings
Vk url also store artist and title.
Delete network requests after use.
Basic cashing.
Support dirs in cashe filename patern. Little refactoring.
For example "%artist / %title" create directory for every artist.
Check cashe if cashing disabled.
Delete file if downloading is failed.
Use temporary file to downloading.

It's prevent using incomplete file because of closing Clementine.
Force cashing.
Full refactoring of caching. Also spell cashe to cache everywhere.
Settings refactoring.
Notify user about cashed file
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