Add support for Creative Mode

[gaurav]

It's unclear exactly how CAM-KP would support Creative Mode, so this would take some thinking about.

Luckily, Creative Mode in TRAPI 1.3 has been architected in such a way that a KP can just ignore it and any client should default to doing "lookup"s only.

Once we know how we want to implement this (or if we explicit want NOT to implement this), we will need to implement the following issues:

• Add knowledge_types to /meta_knowledge_graph https://github.com/NCATSTranslator/ReasonerAPI/pull/333/files
• Add flag for knowledge_type flag for Creative Mode https://github.com/NCATSTranslator/ReasonerAPI/pull/331/files

[gaurav]

Translator Architecture has been coming up with some creative mode queries:

• Creative: Implement "What Chemical increases a particular gene's activity or abundance"? NCATSTranslator/TranslatorArchitecture#79
• Creative: Implement "What Chemical decreases a particular gene's activity or abundance" NCATSTranslator/TranslatorArchitecture#80
• Creative: Implement "What gene's activity or abundance is increased by a particular chemical?" NCATSTranslator/TranslatorArchitecture#81
• Creative: Implement "What gene's activity or abundance is decreased by a particular chemical?" NCATSTranslator/TranslatorArchitecture#82