A more SSL friendly Kandan.

The MusicPlayer, VimeoEmbed and YouTubeEmbed plugins are now protocol
agnostic and will work with SSL/non-SSL Kandan install.

The standard Gravatar address in kandan_settings.yml now defaults to the
SSL Gravatar address.

Closes #322.
Merge pull request #323 from gaelian/kandan-322

A more SSL friendly Kandan.