Additional meta info for Version

[sheridancbio]

Possible enhancements to "Version" class:

• add a "modification_timestamp" property ... to show the time of last modification. Or add a new api endpoint to compute a stable md5checksum of a tree traversal (ordering and concatenating every property of every node in a full tree traversal)
• the api inputs have a "deprecated" flag. We should decide whether to add this to our OncoTreeNode and to the TopBraid concepts. And maybe versions themselves can be deprecated as well (unless we consider all non-current versions other than the most recent one to be deprecated)