Office apps integration based on WOPI protocol: Collabora Office and Office365

From https://wopi.readthedocs.io/projects/wopirest/en/latest/:

The Web Application Open Platform Interface Protocol (WOPI) defines a set of operations that enables a client to access and change files stored by a server. WOPI is a REST-based protocol. It defines a set of REST endpointsas well as operations that can be executed by issuing HTTP requests to those endpoints.

The WOPI protocol is used by Office applications, such as Office Online, to view and edit files that are stored in a cloud service. Thus, Office Online is a WOPI client, while the cloud service that stores the files is a WOPI server, often referred to as a host.

The goal of this issue is to fully support the WOPI protocol in OpenOLAT and implement adapters for both Microsoft Office365 as also Collabora Office (which is based on the free LibreOffice)