change project structure to make more sense

(move wm only stuff to wm dir)

wm/src/essential/mod.rs

@@ -0,0 +1,10 @@
+pub mod desktop_background;
+pub mod taskbar;
+pub mod lock_screen;
+pub mod workspace_indicator;
+pub mod start_menu;
+pub mod onscreen_keyboard;
+
+pub mod about;
+pub mod help;
+