build: use app-id to determine installed icon

This means we don't install org.gnome.Sysprof.svg anymore when building
with -Ddevelopment=true (and vice versa). We do use org.gnome.Sysprof.svg
from libsysprof-ui, but that embeds the appropriate resources.

data/icons/meson.build

@@ -0,0 +1,7 @@
+icondir = join_paths(datadir, 'icons/hicolor')
+
+foreach kind: ['scalable', 'symbolic']
+  install_subdir(kind, install_dir: icondir)
+endforeach
+
+install_data('@0@.svg'.format(app_id), install_dir: join_paths(icondir, 'scalable/apps'))