Put stream downloader options into its own class, and make stream
downloader options global to the stream type rather than specific
to each factory.
Show downloader options in the lbrynet-downloader-gui.
Make a class for downloader option choices, so that the descriptions
can be displayed.
In the console, if there are multiple choices for the download
option, make it a list selected by its index.
Make sure that the ConnectionManager closes properly when some of
the connections fail to open (e.g. due to a host being down)
