Clean up UUID-handling to prepare for future

ts/textsecure/WebAPI.ts

@@ -1083,13 +1083,18 @@ export function initialize({
       );
     }
 
-    async function getSenderCertificate() {
+    async function getSenderCertificate(omitE164?: boolean) {
+      const baseParameters = '?includeUuid=true';
+      const urlParameters = `${baseParameters}${
+        omitE164 ? '&includeE164=false' : ''
+      }`;
+
       return _ajax({
         call: 'deliveryCert',
         httpType: 'GET',
         responseType: 'json',
         validateResponse: { certificate: 'string' },
-        urlParameters: '?includeUuid=true',
+        urlParameters,
       });
     }