UI improvements

Set the windows frame-less and add a custom toolbar. Also force the icon theme and the theme of some widgets. Force some fonts an embed them. Give the used softwares/libs/fonts/themes with their license to be safe.

src/Lib/Ass/AssFactory.cc

@@ -89,7 +89,7 @@ AssFactory::checkValidity() const noexcept
     const SectionContent::const_iterator end = assInfo.end();
     while (it != end) {
         bool ok = false;
-        if (intTypeFields.contains(it.key()) && (it.value().toInt(&ok), !ok)) {
+        if (intTypeFields.contains(it.key()) && (static_cast<void>(it.value().toInt(&ok)), !ok)) {
             qCritical() << it.key() << "is not an integer:" << it.value();
             return false;
         }