Performance improvement: draw less lines to svg

[anonymous]

Current implementation draws all the ticket changes, no matter how small the change is. E.g. If one draws burndown of a project which has 5k tickets and 100k ticket changes, it will easily end to svg with thousands of lines which are not noticeable by end user. It is huge hit to server, may end to big data amounth to be sent over network and also slows down browser.

Drawing could be improbed to take only "visible changes" or abstract drawing somehow. One option could be to draw trend with average values, e.g. 20 bars representing the graph.