When adding an account, the old proccess was: use the (removed) toolbar
to open the New Account dialog, select a provider in that dialog, add
the account and see the newly created account in the panel itself.
That approach had issues, e.g. the user would have to close the dialog
if she mistakenly selected a provider. After moving the provider list
to the panel itself, it doesn't make sense anymore to have another
provider list inside the dialog.
Fix this by moving the new account view to the accounts dialog.
https://bugzilla.gnome.org/show_bug.cgi?id=774222
d50a07da56