implement authenticate user functionality

[juditta99]

API

• install jsonwebtoken
• install bcrypt
• write logic
• write test (.js)
• test logic with node (in terminal)
• write handler for authenticate user
• add endpoint to our index
• test endpoint with curl (.sh)
• write test (.spec.js) using mocha and chai

APP

• create Login page (component) that returns a Form component
• write login user logic
• add onSuccess prop so we navigate to home once logged in correctly