Fix user registration by updating field names to match server field names

[dogezen]

At the moment, the client is using the following field names for user registration:

//src/constants.js
const constants = {
  token: process.env.REACT_APP_USER_TOKEN,
  user: {
    permittedProperties: [
      'firstName',
      'lastName',
      'email',
      'password',
      'biography',
      'github_url'
    ]
  },
  post: {
    permittedProperties: ['content']
  }
}

However, first_name should be firstName and last_name should be lastName.

Fix

• Change src/constants.js to use firstName and lastName
• Change src/components/users/registration/UserForm.js so that all <input> fields have name= properties that match exactly the permittedProperties from constants

Test

Get the user registration working locally.