fix sync

[ichub]

No description provided.

[artwyman]

Low-hanging fruit on my mind to tackle first here, based on Devconnect experience:

• Add validation so a PCDCollection without identity never gets saved/uploaded/downloaded.
• Save/load all user state as a single storage blob so different parts can’t get out of sync.
• Stabilize the order of PCDs in storage, so that reissued tickets moving to the end of the list doesn’t cause extra uploads.
• Detect conflicts (easy now) and perform a simple Union merge (not perfect, but doesn’t lose data).

[artwyman]

The 3rd item above (stabilize order of PCDs in storage) is more complicated than I expected, so has been split out into #1340.

[artwyman]

I've broken out the pieces of this effort, as well as related efforts into separate issues which you can see mentioned above. They have more detail and will allow us to prioritize the different work separately. I'll close out this issue.

Note that the bullet for "Save/load all user state as a single storage blob so different parts can’t get out of sync" didn't get its own issue, but is something I see as a refactoring which may be desirable to enable one of the other work items, primarily #1341