refs #2182
* 🔥 Remove unused options from server init
- this is left over from old code and is now unused
* 🎨 Move knex-migrator check to db health
- Move complex check function into own module
- Call module from server/index.js
- This just improves the readability of server/index.js
* 🔥 Remove old comments
- These comments all make no sense now!
* 🎨 ⏱ Move model init out of promise chain
- Model.init() does not return a promise
- Therefore, we can move it to the top of the init function, outside of the promise change
- This should be a minor optimisation, and again improves readability /clarity of what's happening
* ✨⁉️ Move DBHash init / first run to Settings model
- this structure is left over from when we had code we executed on the first run of Ghost
- the implementation used the API to initialise one setting before populateDefaults is called
- this had lots of dependencies - the whole model, API, and permissions structure had to be initialised for it to work
- the new implementation is simpler, it captures the dbHash getting initialised during populateDefaults()
- it also adds an event, so we can do first-run code later if we really want to (or maybe apps can?!)
- perhaps this is hiding behaviour, and there's a nicer way to do it, but populateDefaults seems like a sane place to populate a default setting 😁
* ⏱ Optimise require order so config is first
- the first require to config will cause the files to be read etc
- this ensures that it happens early, and isn't confusingly timed as part of loading a different module
* 🎨 Simplify settings model changes
