Nuxeo Collabora Online Integration addon

This addon allows to provide resources needed for Nuxeo to use Online's apps in discovery; display
proper icons on relevant buttons (nuxeo-wopi-link); and show correct tooltips for those buttons.

Build dependencies:
 * jar (part of Java)
 * python3

build_addon.py script packs all files and creates the addon package in dest directory.

Install dependencies:
 * nuxeo-wopi addon (https://connect.nuxeo.com/nuxeo/site/marketplace/package/nuxeo-wopi)
 * nuxeo-web-ui addon (part of Nuxeo server)

To install:

 nuxeoctl stop
 nuxeoctl mp-install path/to/collaboraonline-nuxeo-wopi.zip

Configure Nuxeo:

 * edit nuxeo.conf, appending the lines, as described in nuxeo-wopi documentation at
   https://doc.nuxeo.com/nxdoc/nuxeo-office-online-integration/ :

    nuxeo.jwt.secret=<MySecretHere>
    nuxeo.wopi.discoveryURL=https://online_host:port/hosting/discovery

 * Note that you need to make sure that Nuxeo accepts Online's certificate. Also you need to use
   HTTPS with Nuxeo, or else using HTTPS for iframe will be rejected. If you don't use Nuxeo
   recommended method (https://doc.nuxeo.com/nxdoc/http-and-https-reverse-proxy-configuration/),
   e,g. in testing environment, you may need to create a custom keystore for Nuxeo, add the needed
   keys there, and append these lines to nuxeo.conf:

    nuxeo.server.https.port=8443
    nuxeo.server.https.keystoreFile=path/to/custom/keystore
    nuxeo.server.https.keystorePass=keystorePass
    nuxeo.url=https://www.mynuxeoserver.tld:8443/nuxeo

 * You also need to configure Online's loolwsd.xml to accept Nuxeo wopi storage.

Now start Nuxeo:

 nuxeoctl start