Usability: More user-friendly error messages for cloud block instances

[agwells]

I noticed while working on this plugin, that if there's an error connecting to the cloud service while trying to display a page with a cloud block in it, an error like "401 error" or "No access token" is printed on the page. It would probably be more helpful if this error message was printed within the block content itself, or if the block just showed something like "Could not connect to cloud service", and the more technical error went into the error logs instead (via log_warn).