Implement the complete Login and Signup Feature

## Description

Integrate the Login and Signup APIs with the Login and Signup Screen.

## Signup Route

The Signup Route should be refactored to this:

@route POST api/users
@desc Register user
@access Public

This must be a public route, implies no verification is required to access this route.

## Login Route

@route POST api/users/login
@desc Login user
@access Public

## Miscellaneous

Rest all routes should be private and should not be visible unless the User is logged in.