Twitch API: v5 to Helix migration (#1560)

There's a document in src/providers/twitch/api which describes how we interact with the Twitch API.
Keeping this up to date might be a healthy way for us to ensure we keep using the right APIs for the right job.

src/providers/twitch/api/Kraken.hpp

@@ -0,0 +1,61 @@
+#pragma once
+
+#include "common/NetworkRequest.hpp"
+
+#include <QString>
+#include <QStringList>
+#include <QUrlQuery>
+#include <boost/noncopyable.hpp>
+
+#include <functional>
+
+namespace chatterino {
+
+using KrakenFailureCallback = std::function<void()>;
+template <typename... T>
+using ResultCallback = std::function<void(T...)>;
+
+struct KrakenChannel {
+    const QString status;
+
+    KrakenChannel(QJsonObject jsonObject)
+        : status(jsonObject.value("status").toString())
+    {
+    }
+};
+
+struct KrakenUser {
+    const QString createdAt;
+
+    KrakenUser(QJsonObject jsonObject)
+        : createdAt(jsonObject.value("created_at").toString())
+    {
+    }
+};
+
+class Kraken final : boost::noncopyable
+{
+public:
+    // https://dev.twitch.tv/docs/v5/reference/users#follow-channel
+    void getChannel(QString userId,
+                    ResultCallback<KrakenChannel> resultCallback,
+                    KrakenFailureCallback failureCallback);
+
+    // https://dev.twitch.tv/docs/v5/reference/users#get-user-by-id
+    void getUser(QString userId, ResultCallback<KrakenUser> resultCallback,
+                 KrakenFailureCallback failureCallback);
+
+    void update(QString clientId, QString oauthToken);
+
+    static void initialize();
+
+private:
+    NetworkRequest makeRequest(QString url, QUrlQuery urlQuery);
+
+    QString clientId;
+    QString oauthToken;
+};
+
+Kraken *getKraken();
+
+}  // namespace chatterino