Adds Trajectory Replay Functionality

[decodyng]

This PR adds support for visually replaying trajectories saved out according to the structure shown here.

It follows the pattern of demo.ejs to create a separate page on the demo site, /replay, from which you can replay trajectories.

• Slider can jump to arbitrary points in the trajectory
• Single press on L or R arrow keys jumps a step forward or backward
• Holding down L or R arrow keys "speed-runs" forward or backward
• Space bar pauses replay
• "time left" is here used to indicate the steps remaining in the trajectory, which does actually correspond to seconds since we have set 1 second per step in default mode (though this is an easily-modifiable parameter in the code if you want it faster or slower)

Currently the trajectory to be read in is hardcoded in js/overcooked-replay.js; a desired future feature improvement is to allow taking in an arbitrary trajectory file, but that requires me to first figure out more about how JavaScript file readers work.

To build the replay page, run npm run build-replay, and then navigate to localhost:8766/replay.

[decodyng]

Update: Arbitrary trajectory file inputs are now working and code for that has been pushed to the branch

[markkho]

Wow this is slick! Thanks for putting this together - it's definitely much more user friendly than the psiturk version. LGTM

[decodyng]

@rohinmshah Fixed, other than a few cases of my not knowing the correct indentation protocols, and one case of a Chesterton's If Statement

[decodyng]

Ugh, yeah, that sounds both annoying to see and likely fairly annoying to fix, unless there exists some scripts that just do some kind of tab/space standardization