Warning and error message logic for external profiles

- all specs PASS

- logic states if Chaim's Crichton::ExternalDocumentStore.get returns not-nil, meaning that the document was found in the store or cache and thus no messages
- if the above returns nil, and a call to retrieve the file does not return 200, this error is reported:
	ERROR: Invalid external profile url 'http://alps.io/schema.org/Thing/Leviathannn' found in resource 'drd', in state 'activated', transition 'self'
- if 200 is returned then this warning message is reported:
	WARNING: External profile url 'http://www.yahoo.com' exists in resource 'drd', in state 'activated', transition 'self', but is not downloaded. Please run 'rake alps:store_all_external_documents'