feat #1223 font properties for AT widgets

This PR allows users to provide font properties for widgets labels and input fields
Please follow the separation of concerns principle.
Fixed height frames don't use the `${cssPrefix(info)}input` CSS class (cf in `aria.widgets.frames.FixedHeightFrame`), so there should be no rule about this class here.
It should be sufficient to have the rule for the `.${prefix}c` class.