Camera tracking integration

===========================

Initial implementation of graph view for movie tracking data.
Used the same UI-side approach as preview region for sequencer:
create region for graph-related information inside clip editor.

It's easier and nicer than trying to hack graph editor which is
currently designed to work with AnimData only. Trying to make it
more abstract to deal with any kind of data doesn't seem be real
benefit for now.

Currently supported displaying per-frame average error and
selected tracks' movement speed (pixels per frame).

Additional changes:
- Collect per-frame average error after solving.
- Split space clip drawing code into different files.
- Added per-frame average solving error.

release/scripts/modules/bpy_extras/keyconfig_utils.py

@@ -94,6 +94,7 @@ KM_HIERARCHY = [
     ('Console', 'CONSOLE', 'WINDOW', []),
     ('Clip', 'CLIP_EDITOR', 'WINDOW', [
         ('Clip Editor', 'CLIP_EDITOR', 'WINDOW', []),
+        ('Clip Graph Editor', 'CLIP_EDITOR', 'WINDOW', []),
         ]),
 
     ('View3D Gesture Circle', 'EMPTY', 'WINDOW', []),