Add theme toggle

app/src/actions/Global.ts

@@ -1,6 +1,13 @@
-import { ActionTypes } from '../reducers'
+import { ActionTypes, AppState, CustomAction } from '../reducers'
+import { Dispatch } from 'redux';
 
 export const showError = (error?: string) => ({
   error,
   type: ActionTypes.showError,
 })
+
+export const toggleTheme = () => (dispatch: Dispatch<CustomAction>, getState: () => AppState) => {
+  dispatch({
+    type: getState().globalState.theme === 'light' ? ActionTypes.setDarkTheme : ActionTypes.setLightTheme,
+  })
+}