Improve how intents are referred to (i.e. not using strings)

[amitkparekh]

Similar to #24, the way intents are referred to needs to not be using strings so things can be consistent outside of the various services. The path for intents are defined within the Manager service, but they are also referred to within the NLU and NLG service.

Storing the information for the intents outside can ensure that intents are referred to consistently, and that logic for each intent is properly structured.