This patch introduces a lot of things:

1) Implements a proper model-view-controller design for all the paintop
   preset-based properties, such as opacity, flow and size:

      Model --- KisPaintOpSettings
      Controller --- KoResourceManager (also tracks dependencies among
                     the preset and its derived properties, such as
                     opacity, size, flow, composite op)
      View --- KisPaintOpBox.

   Basically, it means that KisPaintOpBox doesn't write to the settings
   directly anymore. Instead, it uses KoResourceManager for that.

2) Well, there are still a couple of flaws in the MVC design. E.g. the
   settings widgets still write directly into the settings bypassing the
   resource managers. To overcome this issue see the next bullet about
   KisResourceUpdateMediator. There is also a bigger problem, the size
   of the brush is still fetched through the access to the GUI elements,
   or, more precisely m_optionsWidget. I don't think...