Resolve optimization in on and optimize

[Swaagie]

Currently the paths of dependencies, css, js and the view are resolved twice. This allows for more flexibility in the use of .on. Per example, providing relative paths, then resolving those via on to make adjustments later on in optimize is a viable strategy. Contour adopts this strategy by replacing parts of the paths.

Double calls however limit performance, so perhaps we could use a flag to acknowledge the use of on, or use the presence of prototype.directory as flag. This should prevent iterating the assets folders twice.