Better error messaging for failed requests about debug-bar-elasticpress

[felipeelia]

Some initial scenarios we can capture:

• post_date_gmt being a text field => It indicates a sync is needed (deleting the index and saving a post should trigger this error)
• sorting on a field that is not indexed

We can start with an array indexed by a regular expression and valued by the message to be displayed. The regex should capture important info and feed it to the message (if it failed due to a meta field, that field should be present in the message)

[felipeelia]

This should now rely on the functionality built in the main plugin (here). Probably some change will be needed there, so we can reuse it here.