Catch and log exceptions thrown when actions can't be created, e.g. under a corrupt database schema

[lsinger]

This PR attempts to address parts of #973 by catching and logging the exceptions that are thrown when actions can't be created. If, e.g., a database schema migration did not complete properly, scheduling an action has been able to render a site inaccessible because exceptions just bubbled up to the user.

This PR explicitly does not solve completing or fixing incomplete schema migrations -- that's a different task. The first step implemented here is to lessen the impact of such issues.

To test this manually, you could take a working site with AS running fine and then drop the priority column. Without this PR the exceptions thrown when trying to schedule actions bubble up to the user, with this PR applied they're merely logged. AS isn't functional then but at least we limit the damage.

Alternatively apply the commits from this branch sequentially and run the test suite in between:

• ff2c680 makes the test suite fail from the uncaught exceptions
• 25a43f2 catches the exceptions and makes the test suite pass
• e1bd2e9 adds some requirements around how we log the exceptions to the tests and makes the test suite fail again
• e5c427f adds the exception message to the log entry and thus makes the test suite pass again
• (27bf749 and b0864e0 are not covered by tests)

Changelog

Fix - Reduce impact when the database schema cannot be modified following an update.

[barryhughes]

This is great, thank you.

• Confirmed a (potentially site-breaking) exception occurs without this change (when the priority column is missing).
• Confirmed an exception does not occur when this branch is checkout out, and that appropriate error messages are logged.