Ok, as it turns out using javascript was not one of by best ideas. I learned the hard way that I have to decide between speed and stability with the two browsers I tested. With Firefox everything was stable, but quite slow. Using Chrome on the other hand sped things up considerably, but it never survived running for more than a couple of hours - without warning the tab would just crash. In the end I figured it is time to use a language which is more stable - this time I opted for Java - which is a nice fit due to its large ecosystem. Another advantage compared to Javascript is the access to the file system, so I can easily use the standard datasets such as MINST - to compare my implementation against the literature.
So the course is plotted, but I'm currently somewhat short on time: in between the end of the year stress - got papers to finish - I seem to be unable to find the proper time to finish this . Well the holidays are up in a week and then I'll have time to work on this - further updates are incoming.