Moves Operator Guide files to its folder

Moves XML files related to Operator Guide to the folder operator-guide. XML
files directly related to Operator Guide are located in operator-guide folder
other XML files common to other books should be placed under common folder.

Change-Id: I67f039e792d0fa8ad832e88a4b48fa87d55c6f4e
Implements: blueprint separate-folders-for-books