Docs: Improved the mock support chapter

This change modifies pretty much the entire mock support chapter.
Main changes to note:

- The repo_lite flag is now described as an "operation mode" of the
  mock repository: When True, the repository is in "lite mode", and
  when False, it is in "full mode". Previously, it has been described
  as a relaxed validation checking, but that is just a side effect
  and not the main purpose. the main purpose of lite mode is to
  allow that the user can go with a mock repository that contains
  only instances, and thus avoids the setup of the class hierarchy
  and of qualifier types in the mock repository.

- The behavior of the faked operations w.r.t. the operation mode
  needed to be clarified for a number of the operations.

- The faked operations are now grouped using the usual names
  for these groups, and the groups have been reordered to match
  the usual ordering for those groups.

Signed-off-by: Andreas Maier <maiera@de.ibm.com>

docs/changes.rst

@@ -404,6 +404,8 @@ Enhancements
   consistency with ignoring the path on
   `CIMInstance.tocimxml()/tocimxmlstr()` (as part of fixing issue #1136).
 
+* Improved the complete pywbem documentation (Issue #1115).
+
 Bug fixes
 ^^^^^^^^^