refs #9742, refs https://github.com/TryGhost/Ghost-CLI/issues/759
- required a reordering of Ghost's bootstrap file, because:
- we have to ensure that no database queries are executed within Ghost during the migrations
- make 3 sections: check if db needs initialisation, bootstrap Ghost with minimal components (db/models, express apps, load settings+theme)
- create a new `migrator` utility, which tells you which state your db is in and offers an API to execute knex-migrator based on this state
- ensure we still detect an incompatible db: you connect your 2.0 blog with a 0.11 database
- enable maintenance mode if migrations are missing
- if the migration have failed, knex-migrator roll auto rollback
- you can automatically switch to 1.0 again
- added socket communication for the CLI
