Label display options & checkbox image-replacement support

This patch adds a widget settings option to include the entity label before/after the rendered element, or hidden.

Also, some themes/modules which replace checkboxes with images rely on a element following the - currently this module inserts a .field-suffix between them. This patch moves the rendered item (and entity label) to the element. Also adds a tiny bit of CSS to display the label inline (and vertical-align checkbox to top).

There's also no need for setting element id/name since core does this for the label.