Update of codebase to conform the rules of Scalastyle

This commit contains:

- Correction of tests that rely on trailing white spaces.
- A fix of a package name in a test unit.
- Removal of trailing white spaces and tabs in the whole project.
  The changes are all done automatically with the following
  commands:

  (Conversion of tabs to white spaces)
  find . -iname "*.scala" -print0 | xargs -0 sed -i 's/\t/  /g'

  (Removal of trailing white spaces)
  find . -iname "*.scala" -print0 | xargs -0 sed -i 's/ *$//'

- To is some content added to an empty Scala file to solve a
  Scalastyle warning.
Add Scalastyle plugin

For the beginning the only rules that are activated are rules that
check for the existence of trailing whitespaces and tabs.

To run the plugin manually simply type in:

  mvn scalastyle:check

This commits contains:

- A Scalastyle configuration file in `sdt.core`. It should be moved
  to the roor directory of Scala IDE once the Scalastyle Eclipse
  plugin is fixed (at the moment it can't read configuration files
  from non Eclipse projects).
- The main POM file is updated with all necessary information to
  run Scalastyle during the build.
- For all including projects, the POM files are updated to run
  Scalastyle during the build.
- The Scalastyle nature and the configuration file for the Scalastyle
  Eclipse plugin is added for each project.