All levels distribution chart on stats page

Description of your request or bug report:

I thought of a chart that I think would be cool on the stats page. Basically, I want to see the total number of books at every single level in a single chart (optionally filterable by book type). Right now the closest charts are the “level distribution” pie chart and the “levels over time” bar graph. This new one would not be broken down by year or group levels together. I think a bar chart would be too busy, so instead a line graph might make the most sense.

Trello link: