Enhancement: Forward share invites to the provider selected in meshdirectory

Added a share invite forward OCM endpoint to the provider links (generated when a user
picks a target provider in the meshdirectory service web interface), together with an
invitation token and originating provider domain passed to the service via query params.

https://github.com/cs3org/reva/pull/1000
https://github.com/sciencemesh/sciencemesh/issues/139
