Exercise 1 & 2 fixups

Hi Mike, 

Thanks for the great time-series workshop this evening, I learnt a lot. I fixed up a few of the typos etc we stumbled across in the class.

I added the 'elec.ts' variable to 2.3 and 2.4 so that they can run standalone and I deleted 2.6 which just seemed to be a duplicate of 2.5.

see you at the next workshop, 

cheers,
Wal