New violations email should contain total violations for each violation type

...type

New violations email only contains information regarding the total violations.
This commit adds support to displaying the total violations for each violation type.

Before the change the email format is like:
      Subject: New violations for project Foo
      From: Sonar

      Project: Foo
      32 new violations introduced since 2012-01-02

      See it in Sonar: http://nemo.sonarsource.org/drilldown/measures/org.sonar.foo:foo?metric=new_violations&period=1

After the change the email format is like:
      Subject: New violations for project Foo
      From: Sonar

      Project: Foo
      32 new violations introduced since 2012-01-02

       Blocker: 12  Critical: 10  Major: 5  Minor: 5  Info: 0

      See it in Sonar: http://nemo.sonarsource.org/drilldown/measures/org.sonar.foo:foo?metric=new_violations&period=1