Improve terminal theming, cursor UX, and size negotiation

src/session_tab.h

@@ -35,6 +35,7 @@ signals:
     void requestReconnect(const SessionConnectOptions& options);
     void requestInput(const QString& input);
     void requestHostKeyConfirmation(bool trustHost);
+    void requestTerminalSize(int columns, int rows);
 
 private slots:
     void onConnectClicked();