Replace lw.svg-parser's curve conversion

[tbfleming]

This is part of the performance issues users have been having with SVG files.

lw.svg-parser produces an insane number of line segments for tiny curves. The original SVG parser used linearizeCubicBezier(), which automatically adapts its resolution to limit segment lengths.

[ghost]

@lautr3k

[tbfleming]

It now handles the test case in #217 better.