Add Navigation Help widget.
Fix incorrect example and destroy method.
Tweak instruction text.
Make help window slightly smaller.
Changes from review.
Fix copy/paste error.
Merge remote-tracking branch 'origin/master' into mouseInstructions

Conflicts:
	CHANGES.md
Minor tweaks.
Add specs for NavigationHelpButton.
Merge pull request #1621 from AnalyticalGraphicsInc/mouseInstructions

Add Navigation Help widget.
Merge remote-tracking branch 'origin/master' into grid-offset
CHANGES.md