Second round of improvements

[alexxbb]

• AssetLibrary::try_create_first() can now crate nodes other than of Object type.
• Functions taking optional parent (Option<NodeHandle>) are now generic and can take HoudiniNode too.
• Improve the error type handling and printing.
• Remove CookOptions arg from HoudiniNode::cook, instead there's new HoudiniNode::cook_with_options.
• Add lots of debug_assert! for input validation.
• ManagerType enum represents a network root node.
• Add several missing geometry APIs.