Removed unused function dateSortInverse()

Was introduced in commit 8de0de11fdfae05f37a10e3b40a59b88157e738e and
is unused since commit 178fccaeea5e2c5cacd6f9a300c6a79511c590fa.
Moved categorySort() and dateSort() and annotated them as private
Started documenting javascript functions
Removed unused function getFeedItem()

Was introduced in commit e9cdfeaf84a5861526db9582a0d09eab49856c13 and
is unused since commit 6877b6bbf6bfd455f3890c9ac1ba68ba6e69406c.