Rewrite IP ban management

This adds a dedicated manager class to handle all ban interactions, which is instantiated and handled by LoginManager.
IPs are now stored in the same format as the datastore, through FileUtils.

Fixes #1032 #587

doc/md/Server-configuration.md

@@ -404,6 +404,8 @@ If Shaarli is served behind a proxy (i.e. there is a proxy server between client
 - `X-Forwarded-Host`
 - `X-Forwarded-For`
 
+In you [Shaarli configuration](Shaarli-configuration) `data/config.json.php`, add the public IP of your proxy under `security.trusted_proxies`.
+
 See also [proxy-related](https://github.com/shaarli/Shaarli/issues?utf8=%E2%9C%93&q=label%3Aproxy+) issues.
 
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