Support imagery rectangles that don't align with tile boundaries.

Fixes #416.
Initial commit to add support for 32 bit index buffers in Terrain Tiles.
Add test for #416.
Update CHANGES.md.
Avoid duplicate intersect.
Encode demo name when building href for demo.

May eventually fix #2182 once it's deployed and re-indexed.
Merge pull request #2181 from AnalyticalGraphicsInc/imageryWithLimitedExtent

Support imagery layer rectangles that don't align with tile boundaries.
Tweak CHANGES.md
Merge pull request #2184 from AnalyticalGraphicsInc/encodeHrefSandcastle

Encode demo name when building href for demo.
Add showcase
Reorganize featured demos
Adjusted ambient lighting to brighten scenes that use terrain vertext lighting.
Merge branch 'terrainIndices32bit' of https://github.com/abwood/cesium into terrainIndices32bit
Fix bugs in ComponentsEntityCollection

1. `onCollectionChanged` handling was not properly resetting a value to undefine for each iteration of a for loop, leading to the first entity incorrectly being the target for all merged properties.
2. Fix bug in `Entity.merge` which was causing custom properties registered on the source entity to not propagate to the target entity if they did not already exist.
3. Added specs to expose both issues.

Fixes #2180
Fix broken includeStart comment
Merge pull request #2187 from AnalyticalGraphicsInc/fixPragma

Fix broken includeStart comment
Cleanup.
Fix color of credits that are text links.
Added unit tests for testing Quantized-Mesh tiles with 32bit indices.  Minor cleanup.
Merge remote-tracking branch 'agi/master' into terrainIndices32bit