Question simplification

Some modifications, mostly on part __Question Simplification__.

I think it's Tom that has written things in Question Simplification section. If you don't agree with what i've deleted/modified, don't hesitate to say it :)

Modifs:
  - the example used is `What is the birth date of the president of the United States?` instead of `What is the birth date of the first president of the United States?`. Indeed, figures are shorter now and it's easier to "run" the algorithm on it.
  - figures have been placed into the text (and not in Appendix, except for the final one). I think if we put figures in appendix they will not be seen (and the text looks better with trees into it :) )


I will read back what i've written sooner. Some things to check : merge(s), consist in/of, ~~Question(s) simplification~~