dropbox: upgrade authorization to latest library version

- Download the latest version of the client libary (1.1.0)
- Register the app in App Console as 'rrss'
- Update manifest to conform to Chrome's new security restrictions
  about web resources accessible from outside the extension
  (loaded by the Dropbox's login completion stage)
dropbox: write data to remote table

- rtable: methods for writing into a remote table
- feeds: write remotely status 'read' by walking over all entries
  at boot time

success: first table created into Dropbox, datastore browser
dropbox: process records fed into the updates listener

- Reconstruct object from list of fields and Dropbox record
dropbox: complete insert/update function

- Use our own m_rss_entry_hash as primary key instead of the auto
  denerated IDs by Dropbox.
- Properly form an object from one remote DB entry for the listener
- Operation "mark as read" updates remote DB
dropbox: synchronized "mark as read"

- rtable: remote listener marshals into local records format
- feed_disp: display remote "mark as read"
- feeds: reflect remote "mark as read" in local db
dropbox: initial synchronization with remote table

- rtable: can generate update events for an entire table
- feeds: at startup time synch with remote table via
  the events listener
dropbox: remote table for rss subscriptions

- Create table at init time
- Send all local unsynchronized subscription entries to rtable
dropbox: handle unsubscriptions and remote tables

- Handle remote subscriptions as events of remote table
- startup: Synchronize local subscriptions
- startup: Delete subscriptions that are not in remote table
- bug: After Dropbox login required a reload. Fixed!
dropbox: move login/logout handler into a devoted object

- Move the code that handles login/logout into a separate object
- Handle the UI for Dropbox menu
dropbox: fix UI area of login/logout

- Add progress indicicator
- Fix alignment of UI area (persistency)
Merge pull request #1 from pmarinov/work-dbox-1

Implement syncronization with Dropbox