Added utilities

What's new:
* Adding logout button, hiding call buttons before login (wasn't being done before - part of https://github.com/opentelecoms-org/jscommunicator/issues/23)
* 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
* Option to clear dialing box after call - or keep last number for redial (https://github.com/opentelecoms-org/jscommunicator/issues/8)
* Show controls on webcam display https://github.com/opentelecoms-org/jscommunicator/issues/4
* Make webcam display size customizable https://github.com/opentelecoms-org/jscommunicator/issues/3
* Extra: make webcam display draggable
* Start sending DTMF as soon as user presses button https://github.com/opentelecoms-org/jscommunicator/issues/13
* Making URIs in event-demo clickable to redial previous or missed calls https://github.com/opentelecoms-org/jscommunicator/issues/2