Merge lp://staging/~jonobacon/ubuntu-accomplishments-viewer/u1-signup into lp://staging/ubuntu-accomplishments-viewer

This branch adds support for signing up from the application if no Ubuntu One account is found. Please note: you should ensure that you also apply the equivilent branch to the daemon: lp:~jonobacon/ubuntu-accomplishments-daemon/u1-signup

This is the user experience: the user does not have an Ubuntu One account. They fire up the accomplishments system and a message explains why Ubuntu One is required and says it will detect an account. If no account is found a native GTK window pops up where the user can sign up, and when they register they are emailed a code that they enter into the app. When the signup process is complete, the app moves on to register the share as normal. While the process is not perfect for 0.2, it works, and in 0.3 we can refine it further: but at least we will know that people without accounts are taken care of.

Some notes:

 * This works by running a new method in the daemon that detects credententials and if credentials are found it triggers a dbus signal (ubuntu_one_account_ready) which then moves the client onto the share setup step.
 * When we detect the credentials, if none are found the signup process continues before the execution continues.
 * The reason we need to detect for an account first is that we don't know up front from the daemon if the user has credentials, as such if they don't have credentials the signup processes is triggered and the signal is generated as normal.