Fixed bugs relating to the spacing/margins around example exercises and ...

These changes get rid of extra spacing around section titles, and examples with exercises. 

These changes are not pulled on Naginata, so that I do not replace Stacey's changes there. When getting to this pull request and if you need to see these changes on Naginata ping me on skype or jabber and I will update Naginata with this branch.

* I want to confirm that I am correct in thinking based on conversations that section > titlepage > abstract( and ::before) is unused in the statistics book, and that replacing that with the section > titlepage > abstract display none is right.