Code Maintenance - Splitting up Armature/Pose Editing Files

This commit splits editarmature.c and poseobject.c into several files, such that
certain types of functionality are (mostly) self-contained within particular
files (instead of being mixed in with other functionality in a large file).

In particular, this was done so that:
1) Armature EditMode tools are now in the armature_*.c files only, and Pose Mode
tools in pose_*.c files only.
     - In one or two cases, this hasn't been possible as the two modes rely on
much of the same shared infrastructure.
2) The "clear loc/rot/scale" operators and pose show/hide are no longer housed
in editarmature.c
3) Selection operators, Transform operators, structural (add/delete) operators,
and supporting utilities for the modes (enter/exit/roll-calculations) are not
all interleaved in an ad-hoc manner

Notes:
* I've tried to ensure that the history of the new files has been maintained by
doing
   svn copy {editarmature.c/poseobject.c} {armature_*.c/pose_*.c}
   Unfortunately, this means that the diffs are a bit messy.
* There should be no functional/logic changes here. Just code moving around and
cosmetic comment tweaks where needed.
* #includes have largely been untouched for now, but could be cleaned up later
* CMake changes untested, but should work in theory.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54913 954f8c5b-7b00-dc11-b283-0030488c597c