Upgrade knockout to 3.2.0

https://github.com/knockout/knockout/releases/tag/v3.2.0
Update CHANGES.md
Upgrade to CodeMirror 4.6

Everything works, except for autocomplete.  More cleanup and testing needed.
Fix Sandcastle autocomplete and doc support

Also remove Cesium-hint.js as it's no longer needed.
Update CHANGES.md

Also remove uneeded CSS class.
Fix gutters.
Merge remote-tracking branch 'origin/master' into codemirror-4.6

Conflicts:
	CHANGES.md
Merge remote-tracking branch 'origin/master' into knockout-3.2.0

Conflicts:
	CHANGES.md
Update simple.czml

This gets rid of curved access lines and is also a much smaller file
due to recent toolchain upgrades.
Support detached ReferenceProperty instances

Previously, ReferenceProperty required that it's reference was always
resolved.  This enforces early failure for bad data (such as a CZML file
that references a non-existent property).  Unfortunately, this lead to
problems when manipulating data on the client that would result in
temporary or permanent detachment of references, for example #2044.

In order to address this, I've made a slight change to the reference
semantics which cause a ReferenceProperty that already has a value
to maintain that value if it ever becomes detached (i.e. the entity
it references is removed from the target collection).  It will also
automatically reattach if the reference becomes valid again.  It
is still an error if a new reference is completely invalid (i.e.
the reference was never resolved a first time).  This still provides
early failure in the cases we want it and more flexibility in the
cases we don't.  However, do to other changes in the property system,
we could propably remove this requirement as well if it ever becomes
a problem.
if we ever
BillboardVisualizer improvements

If a billboard was removed and a new one with the same id readded to a
collection while its events were suspended, the old billboard would not
be properly cleaned up and stay in the scene.
More visualizer cleanup

A continuation of 72c52560b5fd934e941f8c3993974c5fbe847b17 to fix
visualizer behavior when adding/removing entities with the same id while
events are suspended.
Merge remote-tracking branch 'origin/master' into how-did-we-never-notice-this
Merge remote-tracking branch 'origin/master' into knockout-3.2.0

Conflicts:
	CHANGES.md
Merge remote-tracking branch 'origin/master' into codemirror-4.6

Conflicts:
	CHANGES.md
Merge remote-tracking branch 'origin/master' into detached-referenceProperty

Conflicts:
	CHANGES.md
Merge branch 'master' into knockout-3.2.0

Conflicts:
	CHANGES.md
Merge remote-tracking branch 'origin/master' into codemirror-4.6

Conflicts:
	CHANGES.md
Merge remote-tracking branch 'origin/master' into detached-referenceProperty

Conflicts:
	CHANGES.md
Merge pull request #2198 from AnalyticalGraphicsInc/knockout-3.2.0

Upgrade knockout to 3.2.0