Checkstyle plugin

Integrates Checkstyle into Eclipse.

Project homepage: http://eclipse-cs.sourceforge.net/
Automatic update URL: http://eclipse-cs.sourceforge.net/update

Unfortunately, the automatic update URL didn't seem to work properly. So, I had to follow the instructions for manual installation.

Note: Make sure to install version 4.4.3. For some reason, the 5.1.0 version doesn't seem to work well (at least not with the configuration that I'm using).