[MM-40406] Add more singletons, refactor main.ts into pieces, add tests and some cleanup + tests for additional coverage (#1890)

* Refactor main.ts dependencies into singleton pattern

* Split main.ts into testable pieces, some other refactoring for singleton pattern

* Unit tests for main/app/app

* Unit tests for main/app/config

* Unit tests for main/app/initialize

* Unit tests for main/app/intercom

* Unit tests for main/app/utils

* Add some more tests to get to 70% coverage

* Fix for linux

* Fix for alternate data dir paths

* Fix E2E test

src/main/tray/tray.ts

@@ -16,6 +16,7 @@ let trayIcon: Tray;
 let lastStatus = 'normal';
 let lastMessage = app.name;
 
+/* istanbul ignore next */
 export function refreshTrayImages(trayIconTheme: string) {
     const winTheme = nativeTheme.shouldUseDarkColors ? 'dark' : 'light';