Confconsole apt proxy config should check for existing config

[JedMeister]

Currently the Confconsole Apt proxy plugin will generate new config in a (new) file: /etc/apt/apt.conf.d/80proxy.

For example, if you set the proxy as http://example.com:8080, it will generate /etc/apt/apt.conf.d/80proxy with the following content:

Acquire::http::Proxy "http://example.com:8080";

IMO it should check for existing config and offer to update that.

In other words it should grep through all /etc/apt/apt.conf.d/ files for any that contain Acquire::http::Proxy.