Test screen for Code Sources

It would be nice to have a test tab in ZMI to test a code source. This tab would check that the code source properly works by calling test_source, and after would let you input test parameters. If you click on a button test, it would then render the code source using those test parameters (that get extracted, validated and all). This might require an extra test parameter model that would be the path to a Silva object used as 'model' for this test (and a version id too)