Include numpy in intro

[kelle]

Make Intro both an intro to Python and an intro to numpy. Should still be 50 mins.

[eblur]

I think a brief intro to plotting matplotlib is also worthwhile.

[kelle]

I actually think we should drop this material from the one day workshop, as discussed in #59

[pllim]

Should we close this then? I think we have agreed to move ahead with #59.