Limit each trajectory to one projectile

[matthew-blackman]

Create a new trajectory every time a new projecile is fired

[matthew-blackman]

Limiting each trajectory to one projectile has fixed the performance issues in the CODAP wrapper, as well as simplified the model. The wrapper code becomes too complex and non-performant with multiple projectiles per trajectory, so we are moving ahead with the one-projectile-per-trajectory system.

Moving to a one-projectile-per-trajectory system means that the projectileObjects collection in Trajectory is now obsolete. We are going to work to refactor Trajectory and any other files that can be made simpler with the one-projectile-per-trajectory system.

Things to look into in cleaning up these loose ends:

• Trajectory.projectileObjects
• TrajectoryNode.projectileObjectViewsLayer
• Modularity with Trajectory target
• Confirm that numberOfMovingProjectilesProperty still behaves correctly in common model

[matthew-blackman]

I will review individual screens to check if there are still implementations of the old pattern and update to the one-projectile-per-trajectory pattern.

[matthew-blackman]

I went through the Intro, Drag, Vectors, Lab and Stats screens and do not see any remaining structures that are based off the of multiple-projectiles-per-trajectory pattern. Closing this issue.