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

Fixes #416.
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