Added GetNextQuestion logic

Uses quizId and previousQuestionId to find next question. returns null
if no next question found.
Merge branch 'master' of https://github.com/hmatland/Quiz

Conflicts:
	WebApplication1/App_Data/ASPNETDB.MDF
	WebApplication1/App_Data/aspnetdb_log.ldf
	WebApplication1/default.aspx.designer.cs