[backend] support view=json in /lastnotifications
[backend] support keys without content in /lastnotifications
[dist] add backend dependencies to obs-api-deps package
enforce a time in notify events, add back 'block' mode for /lastnotifications
[api] do right locking when changing request or review states
[backend] lastnotifications: improve 'next' logic
[dist] sync obs-api-dep spec file, used from now on from git
[backend] do remote getbinaries and binaryversions requests in chunks

This keeps the URLs small, as we don't know if the remote server
can handle long URLs.
[api] better error message on broken createrepo's
[backend] implement lastnotification pruning
[api] synchronize access to /lastnotifications
[webui,api] move the rdiff function from webui

to api to avoid duplicatin a rather huge function
test