added gpodder package

Hi,

I added a gpodder package. Please keep in mind, this is my first package. So if something is not optimal please notify me and I happily fix it.

Best,
Sven
A sensible default would be `gpodderHome = "$XDG_CONFIG_HOME/gpodder"` and `gpodderDownloadDir = "$XDG_CACHE_HOME/gpodder"` which usually default to `~/.config/gpodder` and `~/.cache/gpodder` respectively. But I don't know how to use the `XDG...` variables and I hesitate to set the directories to the expanded form because people could have changed the default locations of the xdg directories (like myself).