Enable or disable testing for any directory, unit test, or `test_` method in dock

[accmltr]

Making testing for any element and its children optional, will enable people to skip testing for certain parts of their projects which might take a long time to test.

Create a checkbox or visibility icon for each Tree Item and use it to enable or disable that item and its children (recursively) for testing. Also remember the user's settings by saving it to the user preferences file.