This PR refactors most of the codebase to use the new config patterns implemented in #149. Now the core service keeps a copy of the KolideConfig struct, and service methods can reference the configuration in that struct when they need it. The most significant refactoring is in the sessions code, separating the business logic from the storage layer.
- Added all required methods for a UserService
- Added authentication handlers `/api/login` and `/api/logout`
- Added authMiddleware for authentication for `/api/v1/kolide` path
- Added authorization middleware for each endoint
- Added validation middleware for validating API inputs
- Began work on logging middleware
* tests for auth endpoints
* create user test and fatals instead of panics
* more tests
* remove init viper config setting
* stubbing
* more tests
* more tests
* organizing auth and users files
* rest of auth tests
* password reset tests
* renaming campaign to email
* moving session management code to the new kolide/datastore pattern
* removing global configuration variables in favor of config
* moving email operations to package kolide
* moving app to server
* using http.ListenAndServeTLS instead of a method on *gin.Engine
* remove the kolide.go dependency on gin
