#176 Preserve vector topology for SVG exports

[Andrei_n]

The topology of vector layers is not kept when exporting the map as a SVG from Open JUMP. It appears that an uncontrolled (and unnecessary) vector generalization affects the map topology (see attached screenshot). This is most visible when detailed datasets are exported.

[Andrei_n]

[michael michaud]

Partially fixed in the SaveAs Image menu.
SVG output used the same geometry decimator as the screen output.
It now uses a much more precise one (0.001 screen pixel)

Note :
- it is not yet full resolution (would need to make the decimator optional)
- we need to check how Cadplan PrinterPlugIn and Layout Printer work