Token based authentification

Update authentification layer to use token-based authorization in the API.

#### Backend
- [x] Remove session management
- [x] Rewrite API RAML : 
  - [x] ```/api/users``` will become ```/api/account``` : 
      - [x] **POST** ```/api/account``` will create a new user account (registration)
      - [x] **GET**   ```/api/account``` will replace former **GET** ```/api/users/:id``` (read user profile)
      - [x] **PUT**   ```/api/account``` will replace former **PUT** ```/api/users/:id``` (update user profile)
      - [x] **DELETE** ```/api/account``` will replace former **DELETE** ```/api/users/:id``` (delete account)
endpoints
   - [x] ```/api/users/apikeys``` will become ```/api/apikeys```
       - [x] **GET** will list apikeys
       - [x] **POST** will add a new apikey
       - ```/api/apikeys/:apiKeyId``` 
          - [x] **GET** will get apikey detail
          - [x] **DELETE** will delete apikey

#### Frontend
- [x] Remove session management
- [x] Create a Token service to use inside resources calls
- [x] Fix skill queue management