Simplify dialog creation

src/ChatPage.cpp

src/ChatPage.h

src/LoginPage.h

src/MainWindow.cpp

src/MainWindow.h

src/RegisterPage.h

src/TopRoomBar.h

src/dialogs/RoomSettings.cpp

src/dialogs/RoomSettings.h

src/dialogs/UserProfile.cpp

src/dialogs/UserProfile.h

src/timeline/TimelineItem.cpp

src/ui/LoadingIndicator.cpp

src/ui/LoadingIndicator.h

src/ui/OverlayModal.cpp

src/ui/OverlayModal.h