LPS-40606 OpenSocial Gadget Publisher updated to use <aui:button>

Jira ticket: https://issues.liferay.com/browse/LPS-40606
Alternate solution to: https://github.com/noellekimiko/liferay-plugins/pull/6

* Same fix for 6.2.x: https://github.com/jonmak08/liferay-plugins/pull/226https://github.com/jonmak08/liferay-plugins/pull/226
* Tested with a bundle built from https://github.com/liferay/liferay-portal/commit/5a3aa06f217d60005409fa4dc86921623f40dfaf
* Tested in Chrome, Firefox, and IE 8 - 11
* By changing the `<input>` tag to an `<aui:button`> one, the buttons are now styled with bootstrap and are easier to maintain.
* Also, buttons are now responsive to narrower page widths in all browsers except IE 8 
![responsive buttons after](https://cloud.githubusercontent.com/assets/6542536/5056060/2a14185a-6c25-11e4-9607-adebd1e62182.png)

**Potential Problems**
* `<aui:button>` results in an `<a>` tag in all browsers, instead of a `<button>` one as expected. This is in the taglib, not this bugfix, but it is a bit unexpected.