Copied entries will now also be copied to the system clipboard

Allows copy+paste of entries from an archive to a directory, only currently works for copied entries, not directories
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
ZDoom language configurations update
Merge pull request #220 from Blue-Shadow/master

ZDoom language configurations update
Merge branch 'master' of https://github.com/sirjuddington/SLADE into Music