Fetch user's email address on account creation

[Matthew Barnes]

For Evolution integration with UOA, it would be tremendously helpful if the various account plugins fetched the authenticated user's email address and made that available through the accounts API.

Some account plugins already fetch the email address, but then discards the result. The Google plugin, for example, fetches the email address to set the account's display name but doesn't stash the result anywhere that apps can get to it. And extracting critical account info from a display name seems wrong.

http://bazaar.launchpad.net/~online-accounts/account-plugins/trunk/view/head:/qml/google/Main.qml

E-D-S then has to execute the same REST call to obtain the same email address to configure a GMail account.

Basically I'd really like to get rid of this "collect userinfo" function and rely on UOA to do that:

https://git.gnome.org/browse/evolution-data-server/tree/modules/ubuntu-online-accounts/uoa-utils.h

Ideally this should be done for all relevant account plugins, but for Evolution's current needs the plugins to start with would be Google, Windows Live and Yahoo!.