Import remote ioslave from plasma-workspace

As discussed on plasma-devel, the remote:/ ioslave is used also by Dolphin,
so this move will allow to drop plasma-workspace as runtime dependency for Dolphin.

If you are looking for revisions older than this commit, go to the
plasma-workspace repository and use:

git log 81d76cf038898a4172869b1d23b0eb3b9f1b2d2a -- kioslave/remote

Differential Revision: https://phabricator.kde.org/D4690