Some issues in the Pharo-graphics.pdf

[Maiwaiikou]

Hi,

I noticed some issue in the Pharo-graphics pdf.

In section 3.7, we adding callback methods but when we're doing test, we encounter an error 'value has sent to nil' due to 'callbackBlock value: aValue'.
And there is a miss typing problem in 3.8 because we're using BlNumberInputElement but... We want to test our class create before so it's BlIntegerInputElement.