Implement streaming support

This implements support for streaming episodes rather than downloading them
first.
This introduces a new setting: prioritizeStreaming. If it's set to false
(default) then a streaming play button is only added to the EntryPage.  If
it is set to true, then the streaming play button will also appear on the
Entry delegates instead of the download button.
There is a separate setting to decide if streaming is also allowed on
metered connections.

FEATURE: 438864