Setup version for Trrack schema and enable back compatibility

[NateLanza]

The trrack graph should have a version key indicating the Trrack schema version.

Graphs now have no version, so they should be updated to the latest specification on load.

#64 and #65 will change the schema, so start versioning after those are fixed.

For the future, any changes to the schema that can cause version changes should be coupled with logic to update the previous version to the current one. If not possible, explicitly throw an error to alert the user.