First steps to updating skeinforge to release 50

Began to update skeinforge ebuild to release 50, but needs to be adapted
to new portage/ebuild format as well.
Might also need external "psyco" tool for speed up.
Added ebuild for reprappro utils

First version of an ebuild for utilities from RepRapPro (pronterface,
pronsole and printcore). It uses the most recent zip-file from
corresponding GitHub repository.
Working and simplified ebuild for skeinforge 50

This is an working and simplified ebuild for most recent skeinforge
version 50. It does not generate any warnings and should be easily
updateable by simply copy and renaming it to the newest release of
skeinforge.
Merge branch 'skeinforge_upgrade'
Added missing dependencies

Added dependencies for tk use-flag in python (Tkinter) and
app-arch/unzip (to be able to unpack the code archive).
Removed OpenSCAD ebuild

OpenSCAD ebuild was removed as it is already in regular portage
Added slic3r ebuild

Adding a new ebuild for slic3r g-code generator. Use x86 version even
on x64 architecture, as there seems to be no GUI for x64 systems...
More straightforward dependencies and USE-flags

This solves strange way of dependencies were implemented in old ebuild.
Now reprappro depends on skeinforge or slic3r if USE flags are set.
Removing more ebuilds which are already in portage

More ebuilds which are already in portage got removed