NDNts-aux snapshot

[CAWorks-ChrisA]

Includes snapshot program parts 1,2,3 and some leftover debug code (when all testing is good will remove before merge)

• Part 1 (yjsAdaptor): Check the state vector for the snapshot interval, and when the interval is up, publish and update the persistent storage on the blind fetch pointer of the latest snapshot.

• Part 2 (syncAgent + namespace): An additional checker for the snapshot keyword for the existing syncAgent endpoint, and respond by checking persistent storage with the name as the key.

• Detailed explanation of how this is achieved is in the slides and the doc attached below.
• If needed, will move it to a separate function or a separate class/endpoint.

• Part 3 (yjsAdaptor): A callback registered to the syncAgent to handle the topic 'snapshot'. When a member receives a snapshot via blobs, it checks it against its persistent storage blind fetch pointer. If the received snapshot is newer, it will override the pointer with the snapshot it just received.

• Again, this is a rough overview, please consult the slides / docs

Lastly, a minor debug code is added to fetchBlob(), because I found that under heavier loads it is prone to lag and therefore cause problems to the synchronization process.

This pull request is meant to be a work-in-progress, as there are many debug codes to remove and unsafe calls to fix.

Attached are the slides and doc for documentation.
https://docs.google.com/presentation/d/15q8wTChtQtKzaAA1anvDJa1ZNr1DS1Kc67kW6XYghzM/edit?usp=sharing
https://docs.google.com/document/d/1s4pnJS4vSAP_EJD-P0XP6J5osoz8nNgEfLs-HOCDL6U/edit?usp=sharing

[zjkmxy]

UCLA-IRL/ndn-workspace-solid#4

[zjkmxy]

Basically good to me

[zjkmxy]

Please remove other Adam Chen Injection XXX as well. These comments do not explain the purpose of the code and I think is unnecessary.

[zjkmxy]

LGTM now. Let me test this weekend and merge