Add support for lyrics

[danielepintore]

In this pull request I've added support for lyrics.

When we make a scan now we check for lyrics inside the file using taglib, once the scan process in finished we have all lyrics saved on the db so we can retrieve them faster. When we are looking for a lyrics it first checks if there is a embedded lyric, if there is we return that, otherwise it looks for a file SONG_NAME.lrc and reads the lyrics from it. If there isn't a .lrc file an empty response is provided.

I've added support for both getLyrics and getLyricsBySongId methods. I have even created a migration, but i'm not so sure if that works fine maybe give that a double check.

Let me know if there is something to change. P.S. I have used some code from #488