Better dual color prints

Note: this feature is not yet implemented in 2.x, but is in 1.x.

Our clean color algorithm takes several steps towards improving multi-filament print quality. It first orients the print so as to minimize interference between nozzles, and then uses a special travel move optimizer to reduce ooze deposition.

Left: Printing without any optimization. Middle: with ooze shield only (see above). Right: with azimuth optimization and optimized travel moves. This test is using the #3DBenchy benchmark.