Merge pull request #21 from tilo/feature/moving-migrations-into-separate-directory

moving migration template to separate directory and enabling use of mult...
adding reserved_by and reserved_at to push_messages, so multiple daemons can run
processing all available notifications in batches
processing all available notifications in batches
guarding against duplicates
Merge pull request #8 from tilo/feature/add-reservations-to-messages-for-multiple-daemons

Feature/add reservations to messages for multiple daemons