Remove unused imports
Add test paths to 'single' test project config
Remove afterEvaluate closure

Allow Stalker tasks to be added in the configuration step as the
apply method is called instead of after the project has been
evaluated.
Add basic tests for StalkerPlugin
Detect usages of classes that implement an interface

If an interface is implemented by a class, that class is
collected as input to test against the target classpath.

- Add tests
Merge pull request #22 from jle/detect_interface_changes

Detect interface changes