The button can now be used in two different modes. The default behavior
is to include all settings used for configuring
QgsTextFormat/QgsTextRenderer classes. A cut down mode (without settings
for color/buffer/drop shadow/etc) is also available when the resultant
font is to be used only in a QFont object.
A standard widget for configuring text format properties for use
with QgsTextRenderer/QgsTextFormat.
It's modelled heavily off QgsColorButton, and supports lots of nice
things like dragging formats between buttons, copying and pasting
format settings, dropping colors from color buttons, dragging colors
from font buttons to color buttons, directly setting font size
and opacity/color without having to open a dialog.
