Rename bitstring status list concept.

Author: msporny

diagrams/StatusList2021.svg renamed to diagrams/BitstringStatusListConcept.svg

@@ -284,12 +284,12 @@ <h3>Conceptual Framework</h3>
 
         <figure id="bitstring">
           <img style="margin: auto; display: block; width: 75%;"
-               src="diagrams/StatusList2021.svg" alt="diagram showing a
-               list of boxes at the top of the image with two of them in
-               red depicting revoked credentials. Text beside the boxes to the
-               right reads 16 kilobytes. An depiction of the boxes being
-               GZIP compressed into a cylinder on the bottom of the page shows
-               that compression has resulted in a final size of 135 bytes.">
+            src="diagrams/BitstringStatusListConcept.svg" alt="
+          diagram showing a list of boxes at the top of the image with two of
+          them in red depicting revoked credentials. Text beside the boxes to
+          the right reads 16 kilobytes. An depiction of the boxes being GZIP
+          compressed into a cylinder on the bottom of the page shows that
+          compression has resulted in a final size of 135 bytes.">
           <figcaption style="text-align: center;">
             A visual depiction of the concepts outlined in this section.
           </figcaption>