Noise > Bilateral Smoothing: UI adjustments

- Revisit and rename available controls.  Spatial Power has been hidden,
so it can easily be reinstated in the future if desired, but hopefully
this new arrangement strikes a balance of "full power" and not
overwhelming the user...
- Fix Reset values (thanks to @audioglider for catching)
- Add menu icon and change menu name to "Remove Noise"
PDI files: add support for metadata

Now, if a PDI file is based off an image that contained any type of
valid metadata, that metadata will be successfully stored inside the PDI
file in a custom metadata node.

Because PD does not currently allow for direct metadata editing, this
was fairly straightforward, but it will be more complicated in the
future when metadata editing is implemented.  As such, I'll need to come
up with a custom technique for saving a separate list of metadata edits
alongside the original metadata string.  (The save function is already
set up for this.)

Such an approach will make metadata editing non-destructive when done
with PDI files!