Move highlight phrases to new settings system

Add a setting serialize/deserializer for QString
Add constructor to ChatterinoSetting that doesn't take a default value

src/util/serialize-custom.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <QString>
+#include <pajlada/settings/serialize.hpp>
+
+namespace pajlada {
+namespace Settings {
+
+template <>
+struct Serialize<QString> {
+    static rapidjson::Value get(const QString &value, rapidjson::Document::AllocatorType &a)
+    {
+        rapidjson::Value ret(qPrintable(value), a);
+
+        return ret;
+    }
+};
+
+template <>
+struct Deserialize<QString> {
+    static QString get(const rapidjson::Value &value)
+    {
+        if (!value.IsString()) {
+            throw std::runtime_error("Deserialized rapidjson::Value is not a string");
+        }
+
+        return value.GetString();
+    }
+};
+
+}  // namespace Settings
+}  // namespace pajlada