Removed padding of menu bar item in BB10

When adding captions to the items in a screen menu, the text is too low, almost getting of the menu.

![img_00000006](https://cloud.githubusercontent.com/assets/2621975/3928917/c0b47a34-2413-11e4-810b-709c9ebf3b1f.png)

In the CSS rule `.bb-menu-bar-item-caption` at [src/bb10/css/bbUI.css#L653](https://github.com/blackberry/bbUI.js/blob/master/src/bb10/css/bbUI.css#L653) the captions is given 10px of padding at the top and that is pushing the text down.

Removing the padding fixes the position of the captions:

![img_00000004](https://cloud.githubusercontent.com/assets/2621975/3928932/2cfe3b6c-2414-11e4-8968-a9b9804b5736.png)