Add theme enums and platformUtilsService helper (#497)

* Use enum for themes, add getEffectiveTheme

* Update electron and cli to use theme refactor

node/src/cli/services/cliPlatformUtils.service.ts

@@ -1,6 +1,7 @@
 import * as child_process from 'child_process';
 
 import { DeviceType } from 'jslib-common/enums/deviceType';
+import { ThemeType } from 'jslib-common/enums/themeType';
 
 import { PlatformUtilsService } from 'jslib-common/abstractions/platformUtils.service';
 
@@ -135,13 +136,17 @@ export class CliPlatformUtilsService implements PlatformUtilsService {
     }
 
     getDefaultSystemTheme() {
-        return Promise.resolve('light' as 'light' | 'dark');
+        return Promise.resolve(ThemeType.Light as ThemeType.Light | ThemeType.Dark);
     }
 
     onDefaultSystemThemeChange() {
         /* noop */
     }
 
+    getEffectiveTheme() {
+        return Promise.resolve(ThemeType.Light);
+    }
+
     supportsSecureStorage(): boolean {
         return false;
     }