Minor clean up
Replace Java collections by Scala collections
Merge pull request #912 from pdalpra/master

Replace Java collections + clean up
Add foreach loop to iterate through Seq stored in session
Merge pull request #911 from gcoutant/foreach

Add foreach loop to iterate through Seq stored in session, close #906
Use string interpolation in log messages
Fix ConsoleDataWriter + missing logging in FileDataReader
 Use requests response time to compute group duration