Improved format of incoming DBus messages

### Changes

- Cleaned up unit tests
- Cleaned up some of the code: indentation, formatting, etc
- Improved message unmarshaling
 - variants are returned directly, without being wrapped in 2 arrays
 - booleans are returned as true/false - not 1/0 values.
 - arrays of dictionary entries are returned as JS Objects

### Testing

- Added unit tests for my changes. All tests pass.
- Tested interaction with some DBus services: Connman and Ofono.

### Notes

My commits introduce a lot of white space changes (consistent indentation and removal of trailing white space). I hope it is not a problem...