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/Parser/Script/Syntax/ConcreteSyntaxes.spec.ts

@@ -4,7 +4,6 @@ import { ILanguageSyntax } from '@/domain/ScriptCode';
 import { BatchFileSyntax } from '@/application/Parser/Script/Syntax/BatchFileSyntax';
 import { ShellScriptSyntax } from '@/application/Parser/Script/Syntax/ShellScriptSyntax';
 
-
 function getSystemsUnderTest(): ILanguageSyntax[] {
     return [ new BatchFileSyntax(), new ShellScriptSyntax() ];
 }