Improvements to chapter 8 (Reuse and composition at work)

[koendehondt]

This is the first-pass review of chapter 8 "Reuse and composition at work".

There are still issues to tackle in future PRs:

• I think adding numbered labels to the different parts in the first figure would be helpful as a reference for the reader.
• The caption of Figure 8-5 reads: "Live coding your widgets (no it is not openWithSpec but open my friend but the background is supercool!". I understand the super coolness of the photo with the lighthouse in the background, but the code in the photo is wrong and the caption is not very professional. I think we should replace the figure and adapt the caption.
• In section 8.7 "Managing three widgets and their interactions", messages like add: #symbolHere are used, but I think that API had not been explained before.
• In section 8.10 "Changing the layout of a reused widget", the code just above "SHOULD Update" does not handle the case when there is no selection. Shouldn't we add that? Or does that complicate the example?
• Fix "SHOULD Update" and fix "ESTEBAN how can I do" in section 8.11 "Changing layouts".
• In section 8.11 "Changing layouts", there is a message "layoutAlternative1", but the method is not defined.
• In general, we should decide to use "widget" or "presenter". In this PR, I changed some "widget" to "presenter", but not all. Will we use them interchangeably, or is it better to use "presenter" all the way?

[Ducasse]

The changes are good and your questions too.
about the note the latex template supports it but not microdow so I will extend microdown so that we have a simple tag to map the note to the latex macro.
For your questions left tell me what you prefer:
(1) we continue to the point we have several chapters, I print them all and I come to discuss with you about the action. Are you working 100%? Because I thought that you worked 80%.
Or we can do it during a sprint. So let me know.