#53 check in the constructor of MultipleDownload if downloads is not null and added a setStatus() method
#53 in DownloadListChangedEvent added the action ADDED_DOWNLOADS_SUBSEQUENTLY
#53 created the class BackgroundTaskMultipleDownload
#53 added the method addDownloadsSubsequently() to the DownloadManager
#53 added the method addSubsequentDownloads() to DownloadManagerPanel, which is called if the DownloadListChangedEvent ADDED_DOWNLOADS_SUBSEQUENTLY is received
#53 catch exception in BackgroundTaskMultipleDownload which can be thrown due to the FetchDownloadsTask. Also change to the correct status.
#53 MultipleDownload: notify the observers after the status has changed.
#53 in MultipleDownloadPanel added the method addDownloadsToPnlSingleDownloads()
#53 A MultipleDownloadPanel can only be expanded if it actually has encapsulated downloads. If an error occured the error can be shown with a double click.
#53 Changed the transistion from the waiting status to the running status of BackgroundTaskMultipleDownload and the shown message when it is in this status.
#53 in MultipleDownloadPanel set the maximum of the progress bar if the download gets into the running state
#53 made the variable downloadsInSingleDownloadsPanel in MultipleDownloadPanel private
Merge branch 'feature/53-BackgroundTaskMultipleDownload' into dev