Upgrade to video call implementation and dark mode

[mikaelwills]

• Added the infrastructure to be able to upgrade a voice call to a video call. This introduced a new listener function to override 'onNewReinvite(ReInvite event)' which is used by the app that uses the package so it can handle the UI for the upgrade request. Also updated the example app to use the upgrade to video functionality.

• Added darkmode to the example app.

• Refactored how the call screen detects whether it is a voiceOnly call. Previously you could make a video call and the remote side would be told its an audio call. Only when they accept are they suprised to see its a video call. Now on an incoming call it detects if remote has video and for an outgoing call, whether it is video or not is added into the Call object so when you go to call screen you instantly know whether it is voiceOnly or not.

• Added optional functionality to terminate the call if the mediaPort is 0. In some cases when you make an audio call and the port is 0 then if the call goes ahead you're not going to get any audio. But theres also the case where you might want to join a conference call without audio. So i made this an option in the Settings object so it can be used for the first case but not interrupt any other cases.

[mikaelwills]

Hold the merge on this.
I succesfully tested calling and video calling with the example app yesterday but woken up today and audio isnt working in calls. Testing to see if its a server thing or something ive introduced

[mikaelwills]

Can confirm all is working fine with FreePBX over web sockets as well as 3cx over TCP, audio and video calls working fine as well as the upgrade to video.