Add the 'initial-identity' property, which inserts identity for
at startup for event passing, and replaces it with a new child
when the first buffer (and caps) actually arrives.
https://bugzilla.gnome.org/show_bug.cgi?id=599469
fsselector is too close to selector, so import is as autoconvert. Not importing
the history because the directory is also called gst/selector and it fails.