Use dedicated test user to skip jobs during testing

This is not the best.
Update backend's Slim package to 2.4.3
Update backend Httpful\Restful
Add s3 package for managing s3 uploads
Add /upload/android endpoint that accepts apks
Add s3 package for managing s3 uploads, but not as a submodule

This reverts commit 62a729097a81579cd03faa2a287ad87124f2b58e.