Add version handling strategy

[b0rza]

We need to support the following scenarios:

• get and set version from system meta on pull
• skip getting and setting version
  • to faciltate syncs of instances modified prior to last model version (retroactively)
  • to faciltate resync on major schema changes
• skip version only for top level instance being synced, consumables should follow version
  • used in partial syncs on hooks
  • we want to minimize API calls
  • potentially unnecessary, and already enabled by bullet # 1