Save templates client side and add versioning

[LittleEndu]

imo this would have many benefits:

• would allow for an easy check to see if you have the latest template (that is if you know what the latest version nr is, you just check that you have the same nr)
• would allow a rollback if the user finds that the new version doesn't work for them
• would enable some sanity check
  • client can reject individual templates if a "newer" json hosts older template
  • client can ignore a newer json that doesn't bump the version number of a template

This would need to be opt-in and per template, that is:

• user opts in to saving
• template json host opts in to keeping track of versions
  • template isn't version controlled if the version key doesn't exist