add module alias '@tests/'

Alias would remove unnecessary repetitions and less relative paths make changes easier when moving around files. This commit cleans also up some relative paths ('../../../') by using the alias and orders imports. It updates both path alias in tsconfig and module alias in Vue CLI's bundler (vuejs/vue-cli#2398).

tests/unit/application/Environment/Environment.spec.ts

@@ -1,8 +1,9 @@
+import 'mocha';
+import { expect } from 'chai';
 import { IBrowserOsDetector } from '@/application/Environment/BrowserOs/IBrowserOsDetector';
 import { OperatingSystem } from '@/domain/OperatingSystem';
 import { DesktopOsTestCases } from './DesktopOsTestCases';
 import { Environment } from '@/application/Environment/Environment';
-import { expect } from 'chai';
 
 interface EnvironmentVariables {
     window?: any;