#5: Working addon version

This version features a fully working addon version.

This has been tested will all three supported planes, and moving
between them. Only tested in singleplayer.

Known issue:
- If using several playable characters in planes, the script is confused.
  The correct way to fix this is probably to add a check to continuously
  check if the driver (pilot) is a player. An alive check should probably
  also be added.

Some cleaning up is in order before a proper release.

Fixes #5.