Get Scalatra running

[robertPiro]

Currently, the Scalatra dir (./server) is empty and needs to be filled
We also want to set up a port. Is that easy? What did they do in the original Gitpod?

[robertPiro]

Leaving Twirl out was a good choice. It definitely needs Version 1.5.1 as this fixes an error
java.lang.NoSuchMethodError: scala.tools.nsc.Settings.bootclasspath()Lscala/tools/nsc/settings/AbsSettings$AbsSetting;
sbt/sbt#6400
in connexion with sbt.

[robertPiro]

Scalatra is not compiling due to wrong jetty version.
This means that we should drop support for Atmosphere in order to make Scalatra Jetty 10.0 compatible.

Also, since Jetty 11.0 changes the javax namespace to jakarta, the basic servlet api will need to be changed, and the metrics module will need to be reviewed.

scalatra/scalatra#757