Makes sure to reset the value of "global" variables after tests in PageTitleService tests
Creates a TestHelper class with methods for injecting services into tests
Refactors the PageTitleService tests to use the TestHelper class
Refactors the StringService tests to use the TestHelper class
Refactors the tests to utilize the import feature of TypeScript
Creates a method for injecting controllers to the TestHelper
Refactors MainController tests to use the controller injection feature of the TestHelper