Drop websql and store plain file in dataPath

1. Drop websql because it's hard to debug and maintain
2. Use nedb as our db backend (nosql friendly API). Because nedb will
create plain file as db in dataPath, we can debug Atraci more easily
3. fix a bug that when creating playlist, if you type enter (on mac),
then Atraci would jump to white screen without any reason and
Merge pull request #220 from EragonJ/change-db

Drop websql and store plain file in dataPath