Handle null responses from Retrofit

Closes #1
Something something something, README

No, seriously, tweaked the README. That's it.
Merge branch 'master'
Update project for Gradle plugin 0.9+

Neede for Android Studio 0.5+
Reorganize code, retrieve the whole photostream

We don't just retrieve the last 100 photos from Romain's photostream,
we now retrieve all the photos he has. In the future we will probably
have a "Romain's suggested subset" option to exclude the first 300 pics,
as he said "they're not so good anyway".
Fix "per_page" Flickr API param typo in requests
Update README, create CHANGELOG
Add local photostream info caching

Now we only update the photostream once a day, instead of doing it every
time we get the "next" photo. This saves both in network usage and in
update time.
Bump version to 1.1
Update CHANGELOG
Finish 1.1