Extra lectures + lecture notes update

I've added a few extra lectures to the schedule. These will take place on Tuesdays 10-12 in room UE32 in NHA. 

I'll continue tomorrow, finishing fiber products (scheme-theoretic fibers) and then move on to quasi-coherent sheaves.

I've also updated a few of the sections in the lecture notes, in particular the sections about blow-ups and the Proj-construction.