Only copy the doc assets.

The build has been copying everything under doc into the scaladoc distribution, including class files under doc/target. This moves the assets into their own directory, so we can copy just doc/assets and skip doc/target.
Share an executor across all tests.

Eliminated all cases of setting up an executor per test, and all cases of setting up an executor per suite. Now share an executor per run of the tests. This is much easier on JVM resources, so SBT doesn't catastrophically fail as often.

This finishes what was started in 954b55040ece58ccf35f93f7ba6cbb0a94794fc9.
Extract common future/async conversions to library.

closes #54
Merge core and app utilities.

It was gratuitous to have separate projects for these. Core has little utility by itself. There were no saving in transitive dependencies.
Use StoreKit in Finatra Main too.
Extract common Admin handlers.

Both the Finatra and Movies examples duplicated the Admin servlet. And they both had put the admin API on the public HTTP port. The Finagle and Unfiltered example lacked any admin API.

This changes the admin servlet to several Finagle ones and installs them on the admin port of Twitter Server. It does this for the Finagle and Unfiltered examples. TODOs detail what needs to happen with the Finagle and Movies examples.

closes #57
Fix merge build errors.

The build is failing too frequently with "OutOfMemoryError: PermGen space." NPM is printing to the console rather than the log. Unfiltered is now 2.10.