Added strict type checking to the project. (#236)

* Implement strict typing (WIP).

* changes

* Finish type checks

* Fix notification icon, matugen settings and update tsconfig.

* OSD Styling updates and added the ability to configure OSD duration.

lib/icons.ts

@@ -10,7 +10,7 @@ export const substitutes = {
     "preferences-system": "emblem-system-symbolic",
     "com.github.Aylur.ags-symbolic": "controls-symbolic",
     "com.github.Aylur.ags": "controls-symbolic",
-}
+} as const;
 
 export default {
     missing: "image-missing-symbolic",