Download multimedia

[duckbrain]

Many nodes have content of videos, images, and sound files that accompany the text. Videos and images are embedded in the HTML, but are linked to online resources. It would enable a fuller offline experience if these resources could be cached locally.

This will require:

• Parsing the content to find media
• Function to download the media for a node
• Function to get the media for a node, attempting to get it from online if the media is not already cached.