Files view: drop the ASCII column from the change-details hex views

- the modal's hex views carried a 16-byte ASCII column per row; file data is
  rarely text and the column halved the room for the two before/after views,
  so it is gone: `hexImageRows` no longer builds an `ascii` field,
  `hexImageHtml` no longer emits it and the `.hex-ascii` CSS rule is removed
- tests: the hex-row test asserts the field is gone (so it cannot come back
  silently); README/README_RUS wording updated
- SW cache simtrace-analyser-v67 (cosmetic, no version bump)

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simtrace-analyser-v66';
+const CACHE = 'simtrace-analyser-v67';
 
 const PRECACHE = [
     'index.html',