Modelled on OPENVDB_USE_BLOSC, it would be nice to introduce OPENVDB_USE_ZLIB that could be used to make the zlib compression library an optional dependency.

This should be added to the core library, the CMake build system and the OpenVDB Read SOP and should default to ON.

The file dialogs should get the ability to store bookmarks and maybe even to show the default folders of the OS (like Downloads, Pictures, ...)

The custom bookmarks should just be stored as a Cvar (see core/Var.h, or in-game-console command cvarlist) that is separated with ;

At the moment I have a single global nphysics world:

/// `World`-global resource for nphysics `World`.
pub struct WorldResource {
    pub world: World<Real>,
}

But all coordinates given to nphysics are globe-local, because (as far as I know?) nphysics doesn't use any kind of hierarchical coordinate system. (Trying to use some kind of universal coordinates in a solar system w