Implement open-with flow

[glpatcern]

This is to track previously started work, the full story is at pondersource/sciencemesh-php#161

Updated state compared to my last post:

In terms of configuration, Reva is almost complete with some tweaks to be added in https://github.com/cs3org/reva/blob/master/examples/sciencemesh/sciencemesh-apps.toml
The wopiserver deployment should use this config.

In terms of ScienceMesh app developments:

• Persistency of incoming OCM shares - incorrect handling of read-only folders #45
• Set/Unset arbitrary metadata not implemented #43
• The implementation of the CS3API Locks in the nextcloud storage driver in reva.
  • Alternatively / as PoC, Support storages that do not implement the CS3API Lock interface cs3org/wopiserver#125 is an option.
• A hook in the OC/NC frontend for Open remotely, which calls POST /sciencemesh/openinapp to the local reva. This call returns an app-url from the remote site, to be opened in a _blank target (not in an iframe).

For local apps:

• A hook in the OC/NC frontend for Open with app, which calls POST /app/open to the local reva, with a similar response as above.
• The hook could be customized to show Open with <appname> using the reva "discovery" endpoint at /app/list. This is not available for remote apps.