Added value viewer to gt-admin
Fixed datatype bug in geotiff_convert subcommand
Added header caching to Response object.
Set CORS and caching headers on admin site.
Removed unused variable in Server.
Add serialization trait to Operation and Histogram.

All operations (and arguments to operations) must be serializable
for remote execution.  While case classes are automatically serializable,
some classes were being created that did not properly inherit Serializable.
Merge pull request #440 from lossyrob/gt-tool/bug

Fixed datatype bug in geotiff_convert subcommand
Merge pull request #439 from lossyrob/admin/legend

Added value viewer to gt-admin
Merge pull request #442 from lossyrob/small/removeunused

Removed unused variable in Server.
Merge pull request #441 from lossyrob/response/cachedheaders

Added header caching to Response object.
Merge pull request #443 from joshmarcus/topic/serialization

Add serialization trait to Operation and Histogram.