CAS-1271: Maven checkstyle configuration, incorporating a number of conventions

The following rules are in place for now:

1. Using @Test instead of extending TestCase
2. Warnings on Tab indentation
3. Spaces after casts
4. Loggers must be named log
5. Avoid using this.log
6. Avoid checking log levels, use parametric messages. 

The severity level is currently set to warning. We could later on switch to "error" once the codebase is "cleaned".