[MM-39839] Changes for writing unit tests, some re-org (#1849)

* Move tests to individual folders

* Moved e2e tests to e2e folder, fixed lint issues

* Lint fix

docs/development.md

@@ -98,7 +98,7 @@ Mattermost Desktop
 │   ├── common/ - Common JavaScript modules for both Electron's processes.
 │   └── main/ - Implementation of Electron's main process.
 │       └── menus/ - Application menu.
-└── test/ - Automated tests.
+└── e2e/ - Automated tests.
     ├── modules/ - Scripts which are commonly used in tests.
     └── specs/ - Test scripts.
 ```