This removes both the policy-virtual-client.lua and policy-virtual-device.lua
scripts, and creates a new linking/find-virtual-target.lua script to link
clients with virtual session items if one of them can be found. In addition to
this, this patch also ports the policy-virtual-client-links.lua into a new
scripts/rescan-virtual-links.lua to use the event stack. The idea is for the
scripts/link-target.lua to create all links but only activate non virtual links,
and for the scripts/rescan-virtual-links.lua to activate/deactivate virtual
links based on role priorities.
