Tool options panel

Rework UI layout for Creation Tool Options Panels (Circle, Rectangle, Polygon, Gradient, Star, Draw, Spline and  Text) following the design: https://raw.github.com/jcome/synfig_ui/master/plain/ux/tooloptions-window.png
 
To-dos:
- Add tooltips for each option, for easy understanding by user.
- Rethink the options(layer parameters) being exposed or not in tool options panel for each creation tools, do they really help when creating artwork.
- Add angle unit for those widget which needed following parameter panel's implementation.
- Improve widgets which using unit, such as distance widget, their unit should following prefs settings.