Allow dropping connections from the welcome page

This is the last piece required to make sure that we can recover from broken connections, e.g., when the access token is invalid.

src/controller.h

@@ -96,6 +96,8 @@ public:
 
     static void setTestMode(bool testMode);
 
+    Q_INVOKABLE void removeConnection(const QString &userId);
+
 private:
     explicit Controller(QObject *parent = nullptr);
 
@@ -109,6 +111,7 @@ private:
 
     Quotient::AccountRegistry m_accountRegistry;
     QStringList m_accountsLoading;
+    QMap<QString, QPointer<Quotient::Connection>> m_connectionsLoading;
     QString m_endpoint;
 
 private Q_SLOTS: