Unhardcode APPVENDOR here and there

This should have been done in a674498a96.

resources/meson.build

@@ -102,7 +102,11 @@ elif host_platform == 'linux'
 	embedded_files += [
 		[ 'icon_exe_png', rendered_icons['icon_exe'] ],
 		[ 'icon_cps_png', rendered_icons['icon_cps'] ],
-		[ 'save_xml', files('save.xml') ],
+		[ 'save_xml', configure_file(
+			input: 'save.template.xml',
+			output: 'save.xml',
+			configuration: conf_data,
+		) ],
 		[ 'powder_desktop', configure_file(
 			input: 'powder.template.desktop',
 			output: 'powder.desktop',

resources/powder.template.desktop

@@ -2,7 +2,7 @@
 Name=@APPNAME@
 Type=Application
 Comment=@APPCOMMENT@
-MimeType=application/vnd.powdertoy.save;x-scheme-handler/ptsave;
+MimeType=application/vnd.@APPVENDOR@.save;x-scheme-handler/ptsave;
 Categories=Game;Simulation;
 Exec=@APPEXE@ %u
 Icon=@APPVENDOR@-@APPEXE@

resources/save.template.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
-	<mime-type type="application/vnd.powdertoy.save">
+	<mime-type type="application/vnd.@APPVENDOR@.save">
 		<comment>Powder Toy save</comment>
 		<glob pattern="*.cps"/>
 		<glob pattern="*.stm"/>