[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

webpack.config.main.js

@@ -16,7 +16,7 @@ const base = require('./webpack.config.base');
 
 module.exports = merge(base, {
     entry: {
-        index: './src/main/main.ts',
+        index: './src/main/app/index.ts',
         mainWindow: './src/main/preload/mainWindow.js',
         dropdown: './src/main/preload/dropdown.js',
         preload: './src/main/preload/mattermost.js',