Add UI for entering key backup passphrase

src/controller.h

@@ -56,6 +56,8 @@ class Controller : public QObject
 
     Q_PROPERTY(QStringList accountsLoading MEMBER m_accountsLoading NOTIFY accountsLoadingChanged)
 
+    Q_PROPERTY(bool ssssSupported READ ssssSupported CONSTANT)
+
 public:
     static Controller &instance();
     static Controller *create(QQmlEngine *engine, QJSEngine *)
@@ -92,12 +94,16 @@ public:
      */
     static void listenForNotifications();
 
+    Q_INVOKABLE QString loadFileContent(const QString &path) const;
+
     Quotient::AccountRegistry &accounts();
 
     static void setTestMode(bool testMode);
 
     Q_INVOKABLE void removeConnection(const QString &userId);
 
+    bool ssssSupported() const;
+
 private:
     explicit Controller(QObject *parent = nullptr);