Some assorted bugfixes

- Added line of sight check for trap detection, no more "you detect a dissector in the next room through a closed door."

- Made sound of moving rc car translatable.

- Fixes #8011 - Added car horns to scooters.

- Fixes #7946 - Vehicle stereo is independent of engine status (still goes off when the battery is dead). Added energy consumption for stereo (each part of it consumes 1 battery charge).

- Fixes #7549 - Added key bindings for page up/down to the help display.

- Fixes #7372 - Displaying the used and the total volume of the vehicle part. Note: the remaining free volume is *not* displayed because the notation "used-amount/total-amount" (and not "free-amount/total-amount") is also used in the vehicle window for the total volume / fuels etc.