Various documentation improvements

* Added YourKit link to highlights
* Added note about Scala 2.11 to highlights
* Added note about local ivy repo to highlights and migration
* Rewrote documntation on extending Play
specs2 dependencies should be "test" scope
Configure zentasks sample for less and coffeescript
Configure java/zentasks sample for less and coffeescript
Fix possibly null email field in java/zentasks sample
Configure scala/comet-live-monitoring for less and sbt-web
Update js engine for longer timeout and improved logging