introduce concept of autonomous ownship, track sonar selections.
drive controls not visible for autonomous vessel
introduce find-target behaviour, where user has to select particular track on the sonar display
introduce level where user has to read sonar
refactoring missions to create Sonar School
once one find-target objective has been completed, introduce an attribute to allow the selection to be cleared.
Merge branch 'master' into feature/ian/no_drive
Merge branch 'master' into feature/ian/no_drive
make the 0a target a friendly vessel, on the surface
Merge branch 'master' into feature/ian/no_drive
minor typo
improved messages on success/failure, plus fail the test if the wrong sonar track is selected.
improve the test for an autonomous ownship
refactor how we decide whether to show ranging calculator
more maturing the intro levels
Merge branch 'master' into feature/ian/no_drive
use the correct level name
Merge pull request #54 from IanMayo/feature/ian/no_drive

Intro level with autonomous ownship. Only minor code changes, most changes to JSON data files