try to find lrc file in the same directory if no lyric in metadata
Reason for the change
Currently, Elisa only supports lyrics embedded in song the metadata.
This change makes it also look in lrc files in the same directory; FILENAME.lrc
and FILENAME.LRC are supported; other permutations are not, to avoid causing IO
spikes if the directory is large (since we would do this for every song).
Another related change is to treat empty lyrics in metadata as "no lyric" in
datatypes.h. This is because when we're removing the lyric from metadata
we actually just set it to empty string instead of removing the tag.
Test plan
add FILENAME.lrc with lyrics file to the same directory as audio file, open Elisa
and play the song. you should see the lyrics
Bugs fixed
Edited by Nate Graham