Correct "Build Now" and "Build with Parameters" buttons.

Attempts to fix #5 by:

- Adding a `getButtonInfo` function which returns normalized button key/values (i.e. innerHTML, href, hasParams?).
- Following same approach as links in that there is a simple `onclick` vs. `jQuery.click`.
- Delegating to the Jenkins intrinsic `Ajax.Request` for dispatching request.
- Using `hoverNotification`.