1. Extended the vertex export to also work for `po` nodes.
2. Integrated inodes (`p`) and isubnodes (`po`).

* [INODE,SC] Unified the assertion of inodes (`p`) and isubnodes (`po`). They share a lot of properties and this both shrinks the code and eases uniform processing by shared predicates.
* [INODE_EXPORT,EXT] Added compatibility for `po`-node export to vertices.
* [INDOE_EXPORT,SC] The calling of build_vertex/2 was vastly simplified. We now pass values by reference (using a SHA1 hash key) instead of passing a complicated compound term. We are also agnostic as to whether the parent of the built vertex represents an `ihier` or an `inode`.
* [INODE_EXPORT,SC] Created subpredicates for more modular and easy-to-read code: number_of_parent_identity_pairs/3, precision_label/3, and percentage_label/3.
* [INODE_EXPORT,EXT] Added different styles for `p` and `po` nodes.