Add a file information dialog based on ExifTool

Right now, it isn't very pleasing to use.

README.adoc

@@ -5,8 +5,7 @@ fastiv
 raw photos, HEIC, AVIF, WebP, SVG, X11 cursors and TIFF, or whatever gdk-pixbuf
 loads.
 
-It still has some road to go, but it's already become quite usable,
-and it has received basic polishing.
+Its development status can be summarized as '`beta`'.
 
 Non-goals
 ---------
@@ -27,7 +26,7 @@ Build dependencies: Meson, pkg-config +
 Runtime dependencies: gtk+-3.0, glib>=2.64, pixman-1, shared-mime-info,
 spng>=0.7.0, libturbojpeg +
 Optional dependencies: LibRaw, librsvg-2.0, xcursor, libwebp, libheif, libtiff,
-gdk-pixbuf-2.0
+gdk-pixbuf-2.0, ExifTool
 
  $ git clone --recursive https://git.janouch.name/p/fastiv.git
  $ meson builddir