Merge lp://staging/~gary/launchpad/bug750561 into lp://staging/launchpad

[r=henninge][bug=750561] add a spinner for when you delete, edit, or add a structural subscription.

This branch adds a spinner when you delete, edit, or add a structural subscription.

It does this with some simple CSS changes. What I've done seems like a pretty good pattern to follow for how to do this, because it seems very simple: just change classes around to spinner while you are waiting for the work to be done.

I added a couple of JS tests for this. They should be relatively straightforward to read. I added the ability of our LPClient stub to halt execution of the callback so you can examine the intermediate state. In order for the test to pass I had to add a dependency for lp.app.errors to work, and then I had to add some code to clean up the overlay that lp.app.errors adds.

While working on the tests, which involved a fair amount of debugging, I became annoyed and distracted by five errors I was seeing in the Chrome error log (but not in the test results). I traced the problem down to the fact that we were reusing the link for every test, which caused the errors as unpleasant side effects. Therefore, I made our setup code set up the link as well. This seemed to work nicely.

I also needed to simulate a click, and I noticed that there were two approaches to simulating a click in our tests: "Y.Event.simulate(Y.Node.getDOMNode(select_none), 'click');" and "select_none.simulate('click');". The second looked wildly nicer and less error-prone (like forgetting to get the DOM node) so I converted all of the code to use it. FF4 newest, Chrome newest and Safari newest all passed with this clean-up.

This is an incremental branch. In order to completely fix this bug, I will need to also add a spinner for the "muting" code in db-devel. I will do that next.

For QA, you should see the "remove" icon turn into a spinner when you click "Unsubscribe" on [structural subscription target]/+subscriptions (when you are in the proper feature-flagged group); and you should see the "submit" button turn into a spinner when you edit or add a subscription on that page or on the structural subscription target overview or bug pages.

Thank you

Gary