[UI idea] Improve grid layout and stats performance

[Felienne]

Last semester, two student projects ran that implemented something to give teachers a better overview of their students work:

1. The grid:

   

2. The live stats:

   

Both features add value for teachers, which is why we added them, but they also have a number of issues, I am documenting them here, we can surely split them into separate issues.

• The lower left panel more of less offers the same overview as the grid, minus the tick mark option, but they look really different. I propose to move the style from stats to the grid, and then to delete this view from the stats page. I have considered merging it all into one view, but upon further reflection, I think they represent different types of actions, so keeping them separate is better, if the look the same. We can always merge it back in if the rest of the issues have been fixed.
• The live stats uses a selector for levels, the grid (and customization page) use a dropdown, let's make the stats page into a dropdown too
• The performance of the Class Errors is horrible, for my class this results in an error often, or in a few mins (!) wait time. At the very least, we should add a front-end element showing that stuff is loading, but I think a lot of optimizations can be made
• There is weird stuff going on with a database table for errors that I don't understand, we must document that a lot better (although I suspect it can be removed all together since it seems to be used only to show stuff in the front-end?)
• The Class Errors have an action to dismiss, but that never really works for me (could also be performance?)

[Felienne]

I made a few notes about slow lines here @jpelay, maybe that helps! https://github.com/hedyorg/hedy/tree/pretty-grid

I will also continue to figure out what is happening a bit more!

[MarleenGilsing]

I'd like to add that in the grid overview the eyes get in the way of checking off the boxes. I propose that all the colums get the same width to solve this.