fix: revert change of cosmic::Task to cosmic::app::Task

This change caused all uses of `cosmic::Task` to be coerced into a
message type specific to `cosmic::app`. Thus, users were forced to
create messages that are wrapped in `cosmic::app::Message` enums.

src/lib.rs

@@ -22,9 +22,7 @@ pub use app::{Application, ApplicationExt};
 #[cfg(feature = "applet")]
 pub mod applet;
 
-#[cfg(feature = "winit")]
-pub use app::Task;
-
+pub use iced::Task;
 pub mod task;
 
 pub mod config;