[packman] Spring cleaning

[Luigi Baldoni]

  Hi all,
during a boring afternoon I had a look at a few seemingly forgotten
packages that are outdated, don't build or are possibly useless.

I suggest the following changes:

link graphics/darktable to Multimedia/darktable
link network:utilities/youtube-dl to Multimedia/youtube-dl

link openSUSE:Factory/xmlsec1 to Extra/xmlsec1
 (or perhaps delete it outright, nothing depends on it and it's
  available in the main repo since 13.2)

link KDE:Extra/coin to Extra/coin
  (again, nothing seems to depend on it)

Extra/proxychains is no longer maintained, perhaps link it from
network/proxychains-ng ?

Also I fixed Multimedia/gecko-mediaplayer but it's no longer
maintained and debian dropped it (#deb797188).
Is that a potential security concern? Or perhaps it's sufficient
to wait until browsers abandon NPAPI?

Regards