It's quite quite common to use similar macros in the form `log::debug!`
or `glib::clone!`. This MR renames the gst log macros so that we can
`gst::debug!` instead of `gst_debug!` and whithout the need for
`use gst::gst_debug`.
When importing the prelude of a crate like `gst` the `glib` prelude is
provided too. Shedding these imports saves quite a few lines and
adheres to keeping it simple; we're not reexporting base/parent preludes
for no reason :)
