[LimeSurveyUploader] Add Events

[sandra-bre]

• [x] onError(string error, string detail)
• [x] onWarning(string warning, string detail)
• [x] onStartLogin() called when the login process starts
• [x] onLoggedIn() called when the user successfully logged in (else onError should be called)
• [x] onStartLoadQuestions() called when the questions are loaded
• [x] onQuestionsLoaded() called once the questions have been received and setup (else onError should be called)
• [x] onStartSubmission
• [x] onSubmissionFinished