did you find any solution on the not writable issue?
I have a similar problem with my installation:
When I’m trying to upload an image e.g. I can choos the file and click the upload button. After the progress bar finishes I get the filename with the hint: Forbidden.
Why is it forbidden to upload media? I checked the user rights etc.
I found out that I could not make xibo to write into the directory I provided during the installation process. Although I changed the rights in order for everyone to have write and read access.
I also didn’t find the place where to change the path for the library directory.
Finally I did a clean and fresh installation and placed directory somewhere else i.e. …/share