Port IFS Fractal Plug-in to GAction/GMenuModel

This patch attempts to port the IFS Fractal plug-in from GTK2 to GTK3.

In addition to the GtkAction/GtkRadioAction conversion, a deprecated gtk_arrow_new () was also removed and replaced with a GtkImage of an arrow per GTK recommendations.

@Jehan: Hi! How do you want the Open/Save/Reset/OK/Cancel buttons handled? I had to add them in manually since (as far as I know) GtkWindow can't auto-generate them with gimp_dialog_new (). I saw they were added manually in the Unit Editor port, but I wasn't sure if that was the correct approach. (I also wasn't sure if they should be in the header or at the bottom, since there's six buttons total with the Help button)

Also, I noticed similar existing formatting issues as you with the animation-play plug-in, and will try to reformat those as well once this is decided on.