Correct of some bugs and use of Volley Client

Volley Client:
 * Correct a parameter in BASE_URL

Login Activity & Sign In Activity:
 * Use a client to connect to internet.
 * Show a progress dialog during the operation.
 * Error message for failed connections.

Home Activity:
 * Fix a bug that let the user use the application without login.

Manifest:
 * Add permission to access the internet.
Refactor to a better understand of the listener