Notify user of runtime errors

[philippjfr]

Lumen can fail to update for a number of reasons and currently can fail silently when you interact with the application. We want to make sure that users see helpful error messages should something fail. The places where this is most important include

• Pipeline._update_data: This is where most of the updates happen, it fetches data from the source, filters data and applies transforms all of which can fail.
• Download._table_data can fail to export downloads.
• ...

A good way of finding all the places where this may be needed might be to grep for .param.watch and provide nice error handling for all callbacks.

[github-actions]

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