A new menuitem toggles Fullscreen mode, which means that the
menubar is hidden, the window is maximized and window manager
decoration is removed. A new button appears in the navibar
which reverts this process.
Fullscreen relies entirely on the window manager, which has the
advantage that window manager keybindings have the same effect
as activating the Fullscreen menuitem. At the same time this
means that Fullscreen won't work at all without it.
Add default font name and size, minimum font size and encoding
preferences. And implement Middle click goto with a preference.
Also the preferences dialog is a bit cleaned up.
The bookmarks panel can display a tree of bookmarks and allows
editing and deleting of bookmarks via a context menu.
The XBEL implementation has been altered to work with a
reference count model to allow panels to update on their own.
