upgrade web toolkit

[carueda]

As mentioned elsewhere in the wiki, given that Scalatra has not been showing the level of community activity that it enjoyed a while ago, the proposal here is to consider migrating to a much more active and supported web toolkit/framework. Akka HTTP and Play Framework look like among the most attractive alternatives. (Btw, interestingly Play Framework is experimenting with using Akka HTTP as its backend.)

EDIT: Play 2.6 now uses Akka-HTTP