(feat) define title of the missed call notification

[VinceOPS]

Hi Taracque,

I just noticed that the notification created by the plugin (on Android) had its title hardcoded in the Java sources ({appName} call missed). I thought it would be a good idea to allow users defining it themselves as a parameter of endCall (but it will still default to the current value).

Thanks for your work, again.

Regards