Improve error display and handling when creating/editing guide

[durden]

We recently changed the guide submission process to use ajax calls. This works very well, but our error handling and display should be improved. For example, we were previously using flask flash messaging to display errors. This is an easy pattern to use but the downside is the message is only shown for the next request. This means error messages are only shown for a few brief seconds when submitting a new guide.

The ajax call retrieves the error message in the JSON data and shows it briefly before redirecting the user. It would be better if this error message was visible on the page until the user resubmits the guide. This helps the user remember why they are resubmitting.

Truthfully speaking this isn't a big issue since there are so few inputs on the editor page. It's probably difficult to forget why you're resubmitting. However, I think it looks better if the error message is always visible.