Update to Pocket v3 API

This is a pretty big task:

Migrate existing extension users to authorize against new OAuth API (need to get access to this API)
Rewrite API calls to use equivalent API scheme
Redo options screen to remove old authorization info
Clear old authorization info from local storage for migrated users
New API doesn't seem to support stats, so getting a count of all user's posts won't work (would have to sync/store entire list)

kenliu / chromeitlater