Blender Git Loki

Use a new flag in duplicator objects to enable cache reading and avoid
unnecessary dependencies.

This flag will replace the current "read" mode on cache libraries.

Beside enabling cache reading, it also disables the current "fake"
dependencies between duplicators and their group objects. This is
exploiting the layer visibility mechanism in depsgraph to ensure that
animated group objects get evaluated when used by a visible duplicator,
even when they are not themselves visible. These dependencies cause
group object updates even if the duplicator is using cached results.
To avoid this unnecessary overhead and make caching worthwhile we
rebuild depsgraph without these relations when using the cache instead.