Improvements and additions to make smoother plots

[CFretter]

So I added a pre-processing step where the starting image can be blurred to make the squiggle variation smoother. I also added two new line joining styles, pointy and round. To make them possible I also added a tapering down of the lines at beginning and end.

[mitxela]

Hi, I might think about this one for a bit - I'm not too keen on adding more controls to the defaults. I feel like it's already a bit too complicated, I've been pondering getting rid of the min/max brightness since those aren't so useful anyway. Maybe I need to think of a good way of bunching together controls which are less frequently used, but still worth having.

[msurguy]

I like the idea of "Advanced" Controls in a tab underneath the regular controls :)