Add observer condition and generally improve trials UI

[rhoslynroebuck]

Added a new "trials observer" task, which is identical to the trials but the player watches a recording, rather than interacting with a live simulation.

Along with this, we have updated the trials UI, including:

• Updating the text and arrangement of the canvases
• Updating the videos, with specific videos for the controllers and hands condition

[rhoslynroebuck]

This is becoming a beefy pull request, so let's get it merged. The observer task is 'working' in that the VR client and puppeteer clients know how to handle the task. However, work needs to be done on creating the recordings, including: (a) finding a way to 'clean' recorded trajectories of the simulation counter variable (this messes up the simulation counter if it is non-zero) and (b) testing to see how the scaling is set when playing back simulations in-game (the simulation should be recorded and replayed at the same scale as the normal trials task).