Fix #260: Add Auto theme preference to set theme automatically. (#835)

* Auto theme preference added

* Fix lint

* Add and use AUTO from consts

* Add shared custom hook to get current theme

* Moved up 'Auto' choice

* AUTO -> AUTO_THEME_ID & extract useCurrentTheme to file

* Liberalise theme setting

* Add tests

ui/package.json

@@ -30,7 +30,9 @@
   "devDependencies": {
     "@testing-library/jest-dom": "^5.11.9",
     "@testing-library/react": "^11.2.3",
+    "@testing-library/react-hooks": "^5.1.0",
     "@testing-library/user-event": "^12.6.2",
+    "css-mediaquery": "^0.1.2",
     "prettier": "^2.2.1"
   },
   "scripts": {