Nodes can be portals

Portal is a node that may be linked to any other node anywhere in the
playground, not just an adjacent node. Portals are bi-directional and
only ever have two ends.

In the playground file, portal entrance is any character that isn't a
wall, a starting position or a regular node.
And make sure the portal can be used
Worms can now reverse

Reversing will switch the worm's head for its tail, without affecting
the worm in any other way.
Better reverse/stay handling logic
Fix method name
And fix the Scala tool
maven-scala-plugin 2.15.2
Update .gitignore for the Eclipse Scala IDE
Upgrade versions of various Scala tools.
Upgrade Logback
Update team timezone info
Upgrade various plugin versions.