Generic exception message shown for upload timeout errors

[Nightriff]

There are two steps where a timeout can occur, but the add-on currently only explicitly handles one of them.

1. The initial upload times out (not handled)
2. The initial upload finishes, returns an operation id, and polling for the operation to finish times out (handled)

The former throws an asyncio.TimeoutError, which is currently not explicitly handled so it shows the generic "Add-on error" message to the user.