Student replay saving issue

[syuChen1]

Right now we are saving student replay by saving an array of objects that contain the workspace XML text for every action in a session. When the session is long, it may create a request too large for Strapi to handle. Heroku will throw an H18 error when this happened. The request will be killed and the client will be left hanging for 30 seconds.

My temporary resolution is to increase the JSON limit in Strapi to 10MB #406 (https://forum.strapi.io/t/unable-to-post-content-to-strapi-which-is-more-than-1-mb-in-size/4895)

However, a more suitable fix will be to only save action (eg. move x block from x,y to x1,y1) instead of the whole canvas. Need to look closer into Blockly Library and find a way to extract the event and reapply it in the researcher's view.