Bing Maps key changes.

 * New default Bing key (Basic / Public website).
 * Write a message to the console when this default key is used.
 * Add the ability to supply a new default Bing key (and eliminate the
message) by setting a property, in addition to optionally passing it to
the constructor as before.
Consistently call the key a key.
Merge remote-tracking branch 'origin/master' into bingKey
Show the number of messages in the Sandcastle console.

Only switch to it automatically on warnings and errors.
Remove useless line.
Merge remote-tracking branch 'origin/master' into bingKey

Conflicts:
	CHANGES.md
Fix ellipsoid tangent planes for ellipsoids other than the unit sphere.
Merge pull request #1150 from AnalyticalGraphicsInc/tangentPlane

Ellipsoid Tangent Plane
Merge branch 'master' into dynamicScene-es5-properties

Conflicts:
	CHANGES.md
Rename `createObservableProperty` to `createDynamicPropertyDescriptor`
Some changes after review.
Merge remote-tracking branch 'origin/master' into bingKey
Tweak Imagery Layers Sandcastle app so it doesn't Bing-warn.
Break Bing Maps key out of the imagery provider.
Add more detail about setting the defaultKey.
Add a link to bingmapsportal.com in changes.md.
Changes.md improvement.
Reset the message count when clearing messages.
Remove console global.
Add specs for BingMapsApi.