Indicate that something went wrong in the UI, when ECA throws an exception

Problem/Motivation

When executing an ECA VBO, and an ECA Action throws an exception, there is no indication to the end-user that something went wrong.The error is logged into the dblog, but as far as the end-user is concerned, the error is "silent".

Steps to reproduce

• Create an ECA VBO and add it to a view
• In the "VBO: Execute..." event, add an action without a template, or any other ECA configuration that causes an error to be logged to the dblog
• Execute the ECA VBO and see that in the UI, there is no indication of an error.

Proposed resolution

I don't think it would make sense to show the actual Error-Message to the user, but if possible, perhaps to include a generic Error message like: "Something went wrong processing item 3 out of 10". Please contact your site administrator!"
If including the queue position and total number of entries is too difficult to include, then an even more generic message would also be okay.

Remaining tasks

User interface changes

API changes

Data model changes