proftpd- Allow custon config file in text box

[snake98]

It would be nice if you had an option to use a custom config or the web options. this would allow greater flexibility of the ftp program, and only take up a slightly more room in nvram..

example, have check box for "advance config" that grays out the server port, files directory, allow write and anonymous login. It then enables a text box that we can type in the whole configuration file to use for proftpd