New 'extract_images' script

Show_Submission/extract_images: new script to read an HTML file looking
    for 'data' scheme URIs (embedded images), extract them and modify
    the HTML to reflect the new source of the image. At present it
    writes a generated file name with a sequence number in it, but the
    appropriate suffix/extension for the image type. This is an alpha
    version which needs further work.

Show_Submission/parse_JSON: attempting to debug a JSON parsing failure.

Show_Submission/parse_JSON

@@ -361,7 +361,8 @@ try {
     $content = decode_json($json_text);
 }
 catch ($e) {
-    die colored( "Failed to decode the JSON in $infile", 'red' ) . "\n"
+    warn colored( "Failed to decode the JSON in $infile", 'red' ) . "\n";
+    die "Error was: $e\n";
 }
 
 $log->info( $showno, "[$VERSION] Processing $infile" );