reader.closeAll fix and small refactoring

+ combined getAllChannelsByAppId with getAllChannelsByReaderType, since appart from one argumet and 'if clause' the code was the same
+ changed 'for' to Array.prototype methods (forEach and map) in _getChannels and getAllChannelsByAppIdType

Change-Id: I849270849e4416165c2ca2d02ddbaa5804442415