PaintBrush improvement

Currently the paintbrush will be activated when the canvas is clicked on. We need to change this so that only when the paintBrush tool is selected on the toolpalette the paintBrush is allowed to paint on the canvas.

To achieve this check out get_state_flags on this page: http://developer.gnome.org/gtkmm/unstable/classGtk_1_1ToolPalette.html

Inside the "Canvas::on_button_press_event" you will need something like:

if(get_state_flags is active)
{
//our paintbrush drawing code
}