keyboard: allow going back from CCInputChooser via single click
When adding new input sources, the first dialog shows a list of
languages, when single clicking one item you go to a subdialog
that has a 'go back' item, that item only works if double-clicking
it, but that is unintuitive because if you entered the dialog by
single click you also expect the 'go back' button to work by
single click too.
The subdialog is a GtkListBox configured to be double click,
because it has an 'Accept' header bar button and we don't
really want to activate the subdialog items by single click,
but the 'go back' row is special and as explained before it is
expected to work by single click too.
So this commit adds the required single click handler for the
'go back' rows created in CCInputChooser.
user-accounts: Initialize CcAvatarChooser a bit earlier
Fixes following warning when activating Users panel:
user-accounts-cc-panel-WARNING **: Error retrieving app filter for user (null): User 4294967295 does not exist
Initialize CcAvatarChooser a bit earlier so it does
not get used by show_user() before creation.
