account-polld push and account notification

Add a toggle for account-polld to the services in some form ("Push/Poll Notifications"?) to:
account-plugin-twitter: /usr/share/accounts/services/twitter-microblog.service
account-plugin-facebook: /usr/share/accounts/services/facebook-microblog.service

and figure out if on is needed for gmail:
evolution-data-server-online-accounts: /usr/share/accounts/services/google-gmail.service

Also create:
/usr/share/accounts/applications/account-polld.application

http://ralsina.me/stories/push-docs.html

Helpers example: http://paste.ubuntu.com/7814282/

Example click app with helpers: http://bazaar.launchpad.net/~ralsina/+junk/hello-v1/files/head:/

Ref for url-dispathing to the webapps: https://wiki.ubuntu.com/URLDispatcher

Work items:
[sergiusens] Define and write interface: DONE
[sergiusens] Write poll daemon: DONE
[sergiusens] Write tests for poll daemon: TODO
[sergiusens] Hooks to envvars for easier testing: TODO
[sergiusens] Write gmail plugin: INPROGRESS
[jamesh] Write twitter plugin: DONE
[jamesh] Write facebook plugin: DONE
[sergiusens] Add debian packaging: DONE
[sergiusens] UOA service for gmail and application files: DONE
[jamesh] Integrate with signond: DONE
[jamesh] Integrate with accounts-glib: DONE
[sergiusens] Hookup daemon to network and battery status: TODO
[sergiusens] Hookup daemon to powerd: TODO
[sergiusens] Use libclick bindings from push-client to query installation status of target APP_ID: INPROGRESS
Figure out if 1 000 000 000 of requests per day for gmail is enough (and how much is needed if not): TODO
internationalization: TODO
integration tests: TODO
persist status on last retrieved messages in plugins: TODO
write test plan: TODO