Added utilities

* Adding logout button, hiding call buttons before login (wasn't being done before)
* Adding and handling config parameter to make dtmf feedback tones optional when pressing the dialpad as requested in https://github.com/opentelecoms-org/jscommunicator/issues/14
* Optional "remember me" to save display name and sip address as requested in https://github.com/opentelecoms-org/jscommunicator/issues/12
BTW i removed this button as it's rendered useless by the controls automatically displayed on the webcam viewer. the 'controls' atribute inserted in video remoteView displays the controls on load then they disappear and will reappear on mouse hover over display area.