Token based authentification

Update authentification layer to use token-based authorization in the API.

#### Backend
- [x] Remove session management
- [ ] Rewrite API RAML : 
  - [ ] /api/users will become /api/account : 
      - [ ] POST /api/account will create a new user account (registration)
      - [ ] GET   /api/account will replace former GET /api/users/:id (read user profile)
      - [ ] PUT   /api/account will replace former PUT /api/users/:id (update user profile)
      - [ ] DELETE /api/account will replace former DELETE /api/users/:id (delete account)
  - [ ] POST /api/authorize replaces /session and return a token to use in the secured api endpoints
- [ ] Update API middleware to use token based authorization

#### Frontend
- [ ] Remove session management
- [ ] Create a Token service to use inside resources calls