Moves Associate Guide files to its folder

Moves XML files related to the Associate Guide to the folder
associate-guide. XML files directly related to the Associate Guide are
located in the associate-guide folder. Other XML files common to other
books should be placed under a common folder.

Change-Id: Ice1362dd51eacd750a382f20df68a2d17c483f6f
Implements: blueprint separate-folders-for-books