Deprecate CRM_Core_Error::fatal()

CRM_Core_Error::fatal() is kind of crufty.

When hit in the site theme it looks ghastly, and there's no way for the calling code to handle a tool (eg Geocoder/Google.php) which calls ::fatal(). If this pattern was replaced with exceptions, calling code would be better placed to handle it.

Let's make CRM_Core_Error::fatal() deprecated, and have it throw an exception instead CRM-20185

Revisiting the list from CRM-9993, this could then have improved or equivalent behaviour depending on the context:

• ajax/rest: set HTTP code & return JSON with error
• drush, wp, cv: throw an exception, let CLI tool handle it
• in CMS: use CMS to return error
• job: throw an exception, API is calling it?