Remove jQuery UI UI code for remove field etc

Issue - difficult to target correct element in JS/CSS
Cause: I believe markup/styles were copy pasted from jQuery ui. But this is overkill and a pain. We are moving to only using jQuery UI for fields that specifically enqueing it.

Fix - update markup with single button element and add styling.

Bonus: The grey circle delete is non-standard UI for WordPress

![image](https://f.cloud.github.com/assets/494927/1258424/66e36230-2bbd-11e3-8eaa-d289a8c41270.png)

Proposal: something nicer. Perhaps a standard WP Button with an icon? Maybe use the icon for remove image for now and then something nice and flat when we do full MP6 support

eg

![image](https://f.cloud.github.com/assets/494927/1258420/46df7942-2bbd-11e3-9ca8-8bb37aa07d5c.png)