Add HUD when loading propositions

- added MBProgressHUD pod
- when a request to fetch propositions is fired up, an HUD appears on the webView (it disappears when the request finishes to load or when the request fails)
Display photos in candidacies tableView

- added AFNetworking library (bubblewrap does not do asynchronous image download)
- added placeholder image (not sure if it works)
Fix placeholder image in candidacies tableView

- fix placeholder image in candidacies tableView
- add a message to the propositionsViewController hud
Merge pull request #2 from pH-k/motion

Motion