Improvements and rework NG SCANIA I6 sound v1.5

A quick overview about what changed/reworked:
- realistic engine start sound interior/exterior
- realistic idle sound interior
- realistic engine off sound exterior
- added warning sound when turning off engine in the interior
- all sticks and switches recorded and added into the game
- real blinker sound

and much more...

Changelog for Version 1.5:
- added realistic trailer-air-brake sound
- optimized some interior sound levels
- re-recorded blinker stick sound
- new handbrake-stick sounds