* Add a new settings (which needs to be manually set): `security.trusted_proxies`
* On login failure, if the `REMOTE_ADDR` is in the trusted proxies, try to retrieve the forwarded IP in headers.
* If found, the client address is added in ipbans, else we do nothing.
Fixes#409
Going through multiple reverse proxy will store multiple scheme and port in HTTP header separated by a comma. Shaarli will use the first one to generate server_url.
* `get_http_url()` renamed to `get_http_response()`.
* Use the same HTTP context to retrieve response headers and content.
* Follow HTTP 301 and 302 redirections to retrieve the title (default max 3 redirections).
* Add `LinkUtils` to extract titles and charset.
* Try to retrieve charset from HTTP headers first (new), then HTML content.
* Use mb_string to re-encode title if necessary.
