Major: 0.4.9

Updates:
1. Update the downloader cache clear policy.
2. Remove some no use code from xiami lyrics.
Merge branch 'dev' of https://github.com/Kreogist/Mu into dev
Major: 0.4.9

Updates:
1. Fixed some title contains '&' and won't search the lyrics bug.
Merge branch 'dev' of https://github.com/Kreogist/Mu into dev