Display P2PK instead of OP_RETURN

fixes #161

frontend/src/app/shared/pipes/scriptpubkey-type-pipe/scriptpubkey-type.pipe.ts

@@ -9,9 +9,12 @@ export class ScriptpubkeyTypePipe implements PipeTransform {
     switch (value) {
       case 'fee':
         return 'Transaction fee';
+      case 'p2pk':
+        return 'P2PK';
       case 'op_return':
+        return 'OP_RETURN';
       default:
-          return 'OP_RETURN';
+        return value.toUpperCase();
     }
   }