Replace ep_upload with ep_image_upload
Due to frequent crashes https://git.fairkom.net/hosting/DevOps/issues/90 the ep_previewimage plugin had to be de-activated. As this was closely connected to ep_upload. also this was de-activated.
settings.json extended for storage in /mnt/data/etherpad-lite/upload
board.conf for apache extended that this upload directory is served via a symbolic link proxy.
- image icon: mouse-over is saying toolbar instead of upload