Fix Holo Spinners

Fix bug 3321329 - Spinner dropdown does not match widget width

Fix a bug in ListPopupWindow where setContentWidth was misbehaving

Add gravity setting to Spinner. This controls the positioning of the
selected item view within the widget. Holo default is left, legacy
default is center.

In dropdown mode, Spinners now WRAP_CONTENT width based on a limited
set of dropdown content. This means the dropdown can display a
reasonable amount of its content without clipping, while matching
width with the Spinner widget itself.

Change-Id: Ia17fd5f71526548408f4ad3b16bde536b0d3b207