This allows to add pad templates and set metadata in class_init instead of
base_init. base_init is a concept that is not supported by almost all
languages and copying the templates/metadata for subclasses is the more
intuitive way of doing things.
Subclasses can override pad templates of parent classes by adding a new
template with the same now.
Also gst_element_class_add_pad_template() now takes ownership of the
pad template, which was assumed by all code before anyway.
Fixes bug #491501.
Make GstObject extend from GInitiallyUnowned, remove the FLOATING flag and use
GObject methods for managing the floating ref.
Remove class lock, it was a workaround for a glib < 2.8 bug.
Remove the parent-set and parent-unset signals, attempt to implement with notify
but disabled because deadlocks in deep-notify.
