Give Effector its own icon

An E split into its colour channels, with two slices slipped sideways,
replaces the generic applications-graphics icon in the desktop entry and
About Effector, with a one-colour symbolic version for panels. Both are
installed into the hicolor theme; a build run straight from the build tree
falls back to the copy in the sources. The version moves to 0.5.3.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

data/org.effector.Effector.desktop

@@ -4,7 +4,7 @@ Name=Effector
 GenericName=Image Effects
 Comment=Cascade glitch and collage effects over your photographs
 Exec=effector %F
-Icon=applications-graphics
+Icon=org.effector.Effector
 Terminal=false
 Categories=Graphics;2DGraphics;RasterGraphics;GTK;
 MimeType=image/jpeg;image/png;image/webp;image/tiff;image/bmp;