Fixes and updates

[Jasper Huijsmans]

Fixes:
I fixed the pager sizing and minibutton positioning bugs. The graphical
pager now uses the ratio of screen width and height to resize, so the
window previews don't get stretched anymore.

Updates:
I added a dialog to the settings manager. It is probably more a proof of
concept than a finished product. You can popup the dialog by running

$ xfce-settings-show all

The dialog shows a list with available modules (only two at the moment).

For future plugin writers: the plugin dialog should be non-modal, that
is don't use gtk_dialog_run(). I did and it makes the settings manager
dialog insensitive while the plugin dialog runs. 

	Jasper

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