Create SettingsUserController

addresses #2422

- creates settings user controller

- creates user model object

- updates user fixture to be compatible with user model

- updates settings/user template

- add validator to Ember Admin

- use validator to validate user model is valid

- add mock response to /users/me/ path

- creates models/base file for all models to inherit from

- add mock response to /ghost/changepw/ path
Merge pull request #2481 from hswolff/ember-settings-user-updates

Create SettingsUserController