add support for https to ffmpeg

[Former user]

Some sites like sites.google.com only support https protocol, so videos stored there do not play in Serviio.

[Former user]

requires --enable-gnutls (see http://gnutls.org/ which includes ssl support) ref http://forum.serviio.org/viewtopic.php?f=8&t=17933&p=96189&hilit=https#p96189.

[Petr Nejedly]

Issue #705 was marked as a duplicate of this issue.

[Former user]

I've been using zeronoe's 67331 without problems since November 2014

[Petr Nejedly]

Serviio's ffmpeg already included polarssl library, but itr looks like it's not supported by ffmpeg itself (only by librtmp). I did have a look at bundling openssl or gnutls, but both of these increase the FFmpeg binary by at least 6MB, which is not acceptable for the limited usage. So I think currently it'll be up to the users to replace the bundled FFmpeg with another one on their own rick / performance hit.