Add Spanish translation (es_ES) via Qt .ts

Migrate kcc_es.json entries into translations/kcc_es_ES.ts on the latest master.

Co-authored-by: FerdyARTs <86256256+FerdyARTs@users.noreply.github.com>

kindlecomicconverter/i18n.py

@@ -8,6 +8,7 @@ LANGUAGES = {
     'zh_CN': '中文（简体）',
     'ja_JP': '日本語',
     'ko_KR': '한국어',
+    'es_ES': 'Español',
 }
 DEFAULT_LANGUAGE = 'en'