Adds support for the following external gallery hosters
- flickr
- panoramio
- photobucket
- picasa
- windows live

This patch does not do the following
- Support non-public albums on flickr or windows live
- Support guest-link albums on flikr
- Support albums with access keys on photobucket or picasa
- Support albums with custom URL's in photobucket

This patch also doesn't have very good error
handling for the above cases

Based on Gregor Anzelj's branch at
 https://gitorious.org/~anzeljg/mahara/anzeljg-mahara/commits/new_slideshow



Bug #794369

Change-Id: I3a961cd97d21d0a8d5ce2f1a32ef81d7c761facb
Author: Gregor Anzelj <gregor.anzelj@gmail.com>
[hugh@catalyst.net.nz prepared for review, expanded commit msg]
Signed-off-by: Hugh Davenport <hugh@catalyst.net.nz>