Each ui::Window now can have a related native os::Window. This
connection is done through the ui::Display class added recently in
c3d52f0bbe5242923c9e38495e1be1135ca0934f.
* Now the max value in dynamics is equal to the brush size, so changing
the brush size (e.g. switching between pencil/eraser tools) will
change the max brush size (which is the most common parameter to
change)
* Added mini_slider style for min/max brush/angle values
* Fixed some issues clicking outside the dynamics popup