feat #790 Updating the computeSize method in order to consider borders

Updating the computeSize method in order to consider borders and margins.

Close #790
feat #781 CSS Gauge progress bar

Adding the css to be used to make the gauge progress bar instead of using images and sprites.

Close #781
feat #786 Adding skinnable properties for the icon

Close #786
fix #780 Removing overflow property from Select Widget style

Removing the overflow:hidden property from the CSS template of Select widget
feat #779 Adding the new AT flat skin

New flat skin for aria templates

Close #779