Adding drag and drop integration test helpers

[robustdj]

This PR intended adds a drag test helper for integration tests.

For example:

drag('.drag-handle-css-selector', {
  beforeDrop: function() {
    // here would be an opportunity to assert things before dropping
  },
  drop: '.drop-target-selector'
});

[dgavey]

This will be useful, thanks for this. I'll need to test this a bit more and make sure we have some test examples and an updated readme before I can release it though.

[robustdj]

Sounds good, I can help provide that. I just wanted to make sure that the approach was okay, before I dug in and worked on it some more. I'll push a few commits later this week

[robustdj]

@dgavey What can I do to help push this PR through? Add a test that uses the helper and update the README?

[dgavey]

Sorry, kind of dropped the ball on this. We will need some tests that use the helpers to confirm they are working, and some info in the readme under a new tests section would be fantastic.

[robustdj]

@dgavey I just pushed a commit that has tests for the test helpers and documentation in the README. Please take a look when you get a chance and let me know if anything else needs to be added/fixed.

[dgavey]

This is great, thanks so much for this!