Fixed Paperless and Nextcloud behind reverse-proxies

[XobrekX]

I fixed this issue in this commit: Issue #60

[provokateurin]

It is bad for security to have it always enabled.
You should always use the external address of your paperless-ngx instance, to avoid such issues.

[XobrekX]

I configured the external address of my paperless-ngx instance, but as described in the Issue, this is a bug that needs to be fixed for this app.

[provokateurin]

I had a look at the server code for these two options again and I'm still convinced that it's wrong to always enable it. I think there are two possible ways this is happening:

1. Your domain resolves to a local IP address like 127.0.0.1 on the host your Nextcloud is on
2. Your paperless-ngx does a redirect to a local domain (or IP address) like localhost

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