Merge lp://qastaging/~sil/photobomb/publish-via-gwibber-upload into lp://qastaging/photobomb

Publish files via Gwibber's Upload API, if it exists. This will use the user's preferred image publishing location, rather than having a separate one in photobomb, and it offloads all the hard work onto Gwibber.

Testing: make sure you have a newish gwibber (kenvandine's PPA has it for natty). Set your default image uploader to something other than imgur (not sure whether there is gwibber UI for this yet, or what the default in gwibber is, but I think it's yfrog). The image uploader service (if there's not gwibber UI for this) is set in dconf-editor, in /org/gwibber/preferences/image-uploader: you can set it to "ubuntuone" to use U1. Use the Micro Blog menu entry in photobomb to tweet about an image; the URL you get in the gwibber posting widget should be a URL from your chosen posting service, not imgur.

Testing, part 2: with an older gwibber, try using the Micro Blog entry: it should fall back to imgur exactly as it did before, thus not breaking older versions or people's expectations.