Made a few lines more readable.
Added some comments.
Replace hardcode baseUrls out with configuration values.
Minor update with some comments.
Introduced protocol, which makes all the Urls for the requests.
Added model.call and some handlers for the notification related to calls.

I also did some minor cleanup in some other files.
Made a new file Commands, to contains functions like: pickupCall.

New protocol have a few comments.
Added Hangup button. Tried to implement Originate but alice don't have full functionality.
Added all the call Interfaces to Protocol, and some of them in commands.
Tried to implement ParkCall/HoldCall. But Alice complains.
Added Future<bool> to configLoaded for clarity.

Also made some minor log message changes.
Changed URI.isAbsolute() to  URI.isAbsolute. It is no longer a function.
Updated pubspec.lock - do we need to track this file?