Content based hash for taxonomy version info

[brollb]

I recently discovered that the commit hash in webgme is not necessarily content based and is sensitive to import/export. We should replace this hash (or add another) which is deterministic and based on the content of the taxonomy.

[brollb]

This should be doable by defining representations in which changes constitute each of the following:

• major change
• minor change
• isomorphism (or similar concept)?

Once these representations have been defined (and can be generated from the exchange format), we simply can hash them for a "semantic hashing."