ui changes

[c-brenn]

ui updates:

• don't display unidentified drugs in the found drugs panel
• give a more detailed error message when no labels are found in the document
• show an empty DDIs panel when fewer than 2 drugs are identified

spinner bug:

when we refactored the request chain we unfortunately lost an easy way to wait for the chain to end. So the spinner would appear and disappear immediately while the request chain did its work asynchronously.

Added await and async function to everything in the chain so we can get this behaviour back.

Perhaps there's a cleaner solution.

[c-brenn]

goes some of the way to closing #108