adding button event and callrequested event

* Version 1.0.8:
* Date: 21st Feb 2013
* Compatible with Spokes SDK version(s): 2.7.14092.0
* Changed by: Lewis Collins
*   Changes:
*     - Add headset button events via new ButtonPressed event handler in
the wrapper.
*       NOTE: you are advised NOT to use headset buttons e.g. talk
button for
*       call control, but rather use the IncomingCall/OutgoingCall
functions
*       and CallAnswered/CallEnded event handlers. Using talk button
will
*       cause problems with multiline devices as talk button events for
the
*       deskphone (+EHS) will also be received by your app through the
SDK!!!!
*       Also bad interactions can occur with talk button and other
softphones
*       on your system e.g. Lync if you try to use raw button events.
*       You have been warned.
*     - Add CallRequested event handler to obtain user call requested
events from
*       dialpad devices (Calisto P240/800 series)