App architecture modifications.

Now GUI and the app itself is divided into two different binaries.
The app also provides system tray icon.
Whereas the GUI can be used to configure the app.

app/src/tray/menu.rs

@@ -0,0 +1,15 @@
+pub enum TrayMenuItem {
+    Restart,
+    Settings,
+    Exit
+}
+
+impl TrayMenuItem {
+    pub fn label(&self) -> &str {
+        match *self {
+            TrayMenuItem::Restart => "Перезапустить",
+            TrayMenuItem::Settings => "Настройки",
+            TrayMenuItem::Exit => "Выход"
+        }
+    }
+}