Added NbJavaModule.findTestTaskForSourceSet
Refactored StandardTaskVariable.
Minor refactor in GradleJavaBuiltInCommands.
JavaTestModel is now actually requested by JavaExtension.
Issue #116: Test, Run/Debug Single Test, Run/Debug Single Test Method should now recognize that they are in a source set of test other than test (for example: "integTest"). Ther are still some problems to be solved:

- NetBeans does not allow to add unit test files to test packages other than the default one.
- NetBeans disables the single test method tests.
- Test Results window might not recognize the xml output folder for test tasks (other than the default test).
- The project's context menu should list all kinds of test tasks.