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
Update simple.czml

This gets rid of curved access lines and is also a much smaller file
due to recent toolchain upgrades.
Merge remote-tracking branch 'origin/master' into codemirror-4.6

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

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

Conflicts:
	CHANGES.md
Merge pull request #2210 from AnalyticalGraphicsInc/simple-czml

Update simple.czml
Merge remote-tracking branch 'origin/master' into codemirror-4.6
Merge pull request #2201 from AnalyticalGraphicsInc/codemirror-4.6

Upgrade CodeMirror to 4.6
Merge master to detached-referenceProperty