wpg-import: fix color swapping for polygon

the fill color was derived from stroke color and vice versa
vdx: export only visible layers
[cleanup] remove EML.sheet.in

Apparently unused and unreferenced since 2001
Bug 731684 - Parse style from root node, too.

All the style attributes can be available with the svg element already.
Apparently no commonly used so not noticed with all the test files up
until now. According to https://bugzilla.gnome.org/show_bug.cgi?id=731684
Google Drive is using this pattern.
DiaRenderer: simplify arrow drawing with combined fill/stroke calls
Bug 731154 - unconnect when nudging object with cursor keys

otherwise the movement will only be temporary for connected objects.
https://bugzilla.gnome.org/show_bug.cgi?id=731154