GH-4071 Heavily refactor and rearchitect account system

This makes the account system much more modular
and makes it treat errors as something recoverable,
unless they come directly from the MSA refresh token
becoming invalid.

launcher/minecraft/auth/flows/AuthFlow.cpp

@@ -0,0 +1,71 @@
+#include <QNetworkAccessManager>
+#include <QNetworkRequest>
+#include <QNetworkReply>
+#include <QDebug>
+
+#include "AuthFlow.h"
+#include "katabasis/Globals.h"
+
+#include <Application.h>
+
+AuthFlow::AuthFlow(AccountData * data, QObject *parent) :
+    AccountTask(data, parent)
+{
+}
+
+void AuthFlow::succeed() {
+    m_data->validity_ = Katabasis::Validity::Certain;
+    changeState(
+        AccountTaskState::STATE_SUCCEEDED,
+        tr("Finished all authentication steps")
+    );
+}
+
+void AuthFlow::executeTask() {
+    if(m_currentStep) {
+        return;
+    }
+    changeState(AccountTaskState::STATE_WORKING, tr("Initializing"));
+    nextStep();
+}
+
+void AuthFlow::nextStep() {
+    if(m_steps.size() == 0) {
+        // we got to the end without an incident... assume this is all.
+        m_currentStep.reset();
+        succeed();
+        return;
+    }
+    m_currentStep = m_steps.front();
+    qDebug() << "AuthFlow:" << m_currentStep->describe();
+    m_steps.pop_front();
+    connect(m_currentStep.get(), &AuthStep::finished, this, &AuthFlow::stepFinished);
+    connect(m_currentStep.get(), &AuthStep::showVerificationUriAndCode, this, &AuthFlow::showVerificationUriAndCode);
+    connect(m_currentStep.get(), &AuthStep::hideVerificationUriAndCode, this, &AuthFlow::hideVerificationUriAndCode);
+
+    m_currentStep->perform();
+}
+
+
+QString AuthFlow::getStateMessage() const {
+    switch (m_taskState)
+    {
+        case AccountTaskState::STATE_WORKING: {
+            if(m_currentStep) {
+                return m_currentStep->describe();
+            }
+            else {
+                return tr("Working...");
+            }
+        }
+        default: {
+            return AccountTask::getStateMessage();
+        }
+    }
+}
+
+void AuthFlow::stepFinished(AccountTaskState resultingState, QString message) {
+    if(changeState(resultingState, message)) {
+        nextStep();
+    }
+}