"Multimaterial printer switches filament at the wrong time during a print"
https://github.com/prusa3d/Slic3r/issues/607
There was a single layer between the raft top and the object first layer
missing on the wipe tower, and after this missing layer all the tool
changes were shifted by one layer, meaning two color print had the colors
switched.
https://github.com/prusa3d/Slic3r/issues/324
Implemented a correct layer height preview for the wipe tower layers,
if the wipe tower layer height is not constant due to the application
of raft.