close: Clear previous highlights before displaying popup corrections

Closes #2

service.js

@@ -428,6 +428,9 @@ class BesService {
    */
   popupCorrectionPanel(el, match, source, highlightEl) {
     const popup = document.querySelector('bes-popup-el')
+    document.querySelectorAll('.bes-mistake-highlight-selected').forEach(el => {
+      el.classList.remove('bes-mistake-highlight-selected')
+    })
     popup.changeMessage(match.match.message)
     popup.appendReplacements(el, match, this, this.isContentEditable())
     popup.show(source.clientX, source.clientY, highlightEl)