Concurrent map feature

Untill last commit there were maps with concurrency capability via [cake](https://github.com/spring-projects/spring-scala/blob/3b6ab283cd58a68ab185dc6f6280d65e30aa0bda/src/main/scala/org/springframework/scala/beans/factory/function/InitDestroyFunctionBeanPostProcessor.scala#L46-L50) pattern.

But such trait was deprecated since `2.11`. Thus it's usage is not recommended anymore.

I'm not sure, why it was necessary to have those value synchronized in the first place (perhaps, because values are public) , but I'd suggest to use instances of `java.util.concurrent.ConcurrentHashMap`, which are naturally converted with [Scala Collection Conversions](http://www.scala-lang.org/api/current/index.html#scala.collection.JavaConversions$).