Move the dock window related themeing namely default dock heght and
font scale from GimpDock to GimpDockWindow to get rid of yet another
GtkWindow dependency from GimpDock.
Note that this change requires gtkrc updates where "GimpDock::" needs
to be repaced with "GimpDockWindow::".
Add a GimpDialogFactory property to GimpDockWindow so that it can get
rid of its GimpDock dependency. We need to call the property
"gimp-dialog-factory" instead of "dialog-factory" though as long as
GimpDock subclasses GimpDockWindow.
Move the GimpUIManager from GimpImageDock to GimpDockWindow. This
includes making the ui_manager_name class-member of GimpImageDock a
normal instance member of GimpDockWindow since the UI manager name no
longer can be configured at the class level.
The GimpDockWindow will need to have a GimpContext so add such a
property but call it "gimp-context" for now to avoid clashing with
"context" of GimpDock.
Introduce GimpDockWindow and make GimpDock inherit from it. Right now
it is just a GimpWindow, but window logic from GimpDock and subclasses
will gradually be moved here so that we eventually can make GimpDock a
GtkBin. That in turn will allow us to put several GimpDocks next to
each other in columns, or GimpDocks in an image window.
