Update folder 1 to only import FBP or FDK from the recon module

[lauramurgatroyd]

Closes #240

[MargaretDuff]

I have tested notebook 3 and 4, with no issues, but can't test 5 at the moment because I am running some experiments over the weekend. I can try again next week, unless someone else has time?

[hrobarts]

Tested 5 and it looks good to me.
Is it worth adding something in the "Offset initial angle to align reconstruction" to say why we're doing this (i.e. so we can crop the reconstruction volume later)?

[lauramurgatroyd]

Forgot to update the exercise notebooks.

We can put this on hold until after the training, or just add text explaining the different reconstruction imports as suggested in the issue