If an invalid stream descriptor hash is entered, abort and
give a useful error.
If a name doesn't resolve, abort and give a useful error.
If a name resolves to something invalid, abort and give a useful error.
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)
