gvle: fix the saving of a new vpz file & fix the "new file" feature & ...

to fix the bug, the new package system, where binaries are separated
from sources, has been apllied.
(Closes #105)
When creating a new file from the file treeview, the Editor did not
initialize the document when it was not a VPZ.
(Closes #109)
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)