Working *.epub to *.kepub.epub file conversions when
using a Kobo reader. Updated docker file to include
`kepubify` to convert to kepub. If not available the
file is just sent without conversion.
We now allow multiple OPDS feeds to be pre-defined and displayed
on the homepage. As a result we need to pass the feed navigation
URLs via query parameter rather than a subpath which would only
support proxying to a single OPDS feed.
The feed is passed via the q= query parameter and any relative
links from the OPDS XML are resolved to a complete URL with
domain / scheme.
We also check the "Content-Type" header in the response
received from the OPDS feed to determine whether to parse
an OPDS catalog or just proxy the raw response back (images / files).
