Implement basic kinto support logic

[linuxwolf]

In service to sync, implement the basic communications between the on-device cache and the remote kinto service.

The intent is to:

• retrieve records from the remote service and apply them locally
• publish local changes to the remote service
• track timestamps

If any conflicts occur, the local change will overwrite the remote change.

Related

• Cloud storage of saved credentials so that they can be accessed from any supported platforms (a single database of credentials for each user) #50
• Implement basic kinto support logic #80 (conflict resolution)

[linuxwolf]

Blocked by mozilla-lockwise/lockbox-extension#489