quiz: add explanation
update Entity Framework
quiz: move maxDropCount to quiz
extract QuizModel from CoursePageModel
db: remove useless courseId from queries
*If we know slideId we will know courseId
update dependence version of entity framework and add indexes to db
Merge branch 'newEF'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/uLearn/Quizes/Quiz.cs
Merge pull request #3 from Tinkturianec/master

quizzes: add explanation
new EF => Indeces