Proper spacing for Anki in {furigana-plain}

This should fix #264 

Note it does not address broken segmentation, just representation
within Anki itself to work properly.

ext/bg/js/handlebars.js

@@ -49,13 +49,13 @@ function handlebarsFuriganaPlain(options) {
     let result = '';
     for (const seg of segs) {
         if (seg.furigana) {
-            result += `${seg.text}[${seg.furigana}]`;
+            result += ` ${seg.text}[${seg.furigana}]`;
         } else {
             result += seg.text;
         }
     }
 
-    return result;
+    return result.trimLeft();
 }
 
 function handlebarsKanjiLinks(options) {