basic style panel

- created StylePanel, an HTML viewer for styles
- created XStyleButton - a webcomponent for showing an example of a
style e.g. a rectangle with some text and a label
- style now has an explicit drawShape() and drawFont() for setting the
styles for fonts and shapes independently
- panZoom now must be passed into the draw function for a shape (this
permits us to draw shapes without panzoom by using the g_noPanZoom
variable)