gvle: fix the Preferences Dialog

The line with scale widget was not configured, and as soon as a
preference was changed, even a color, the line width was set to 0.
(Closes #108)
gvle: fix header guard fail

ifndef had been made on the wrong macro.
gvle: add the adjustment and zoom managment

When switching the view type from "complete" to "simple" and reverse,
the zoom setting is keeped. And the adjustment of diagram inside the
graphical view is keeped also. By the way, each coupled model manage
its own zoom and adjusments.
(Closes #110)