Making the Image Action Use Less Markup and On By Default

[psionic-k]

Instead of:

** Standalone Image
:PROPERTIES:
:DSLIDE_ACTIONS: dslide-action-image :slide-display nil
:END:
You can show images without them being visible on the slide.  A way to achieve a similar effect is to have a child heading with no slide action and only images.
#+attr_html: :width 50%
[[./images/yuki-o-yak.jpeg]]

We want:

** Standalone Image
You can show images without them being visible on the slide.  A way to achieve a similar effect is to have a child heading with no slide action and only images.
#+attr_dslide: :slide-display nil
#+attr_html: :width 50%
[[./images/yuki-o-yak.jpeg]]

And if :slide-display nil is unneeded, using default configurations for the action's slots (which need customize variables), then all you need is:

You can show images without them being visible on the slide.  A way to achieve a similar effect is to have a child heading with no slide action and only images.
#+attr_html: :width 50%
[[./images/yuki-o-yak.jpeg]]

Which is zero configuration 🎉

[psionic-k]

Only thing remaining is a way to annotate specific images and ignore certain images entirely.

Likely some progress on #19 is necessary to completely finish.