Update presentations.md
Merge pull request #23 from merilainen-metropolia/patch-1

Update presentations.md
Tasks for today
Video link was in a wrong place
Added quizzes folder and empty npm-commands.md page.
Presentation dates added
Valittiin aiheet
Merge pull request #38 from Markoham/master

Presentation dates added
Merge pull request #39 from anttev/master

Valittiin aiheet
Link to example repository
A link
Code examples for yesterdays lecture
Link section to all lectures
Starting to make a quiz #40
Quiz time #40
Few words of explanation
Removed file.
Merge remote-tracking branch 'upstream/master'
Added npm quiz #25
Testing .md file formatting.