Add a test case to an existing test suite

[dmcassel]

The mlGenerateUnitTestSuite task will create a new test suite, but if you give it the name of an existing suite it will overwrite the setup and teardown modules. Allow generation of a new test case. This could be done a couple ways:

1. Modify mlGenerateUnitTestSuite so that if the test suite already exists, it creates the new test case and skips all the setup/teardown.
2. Create a new task for generating only test cases.

[rjrudin]

I think approach 1 would work, where the task would say - if the directory exists and there's at least one file in it, then only generate the test module.

[rjrudin]

@dmcassel I'm wondering about the value of this now - in practice, I just copy/paste an existing test, as that is likely to already be importing other libraries that are helpful for my tests. That seems easier than having to remember a Gradle task name and type out the correct arguments.

[dmcassel]

@rjrudin fair enough. Is it worth having the mlGenerateUnitTestSuite task see that the target directory already exists and decline to go further, to avoid overwriting things? Or good enough to rely on git's ability to restore?