no issue
The `settings` service has been a source of confusion when writing with modern Ember patterns because it's use of the deprecated `ProxyMixin` forced all property access/setting to go via `.get()` and `.set()` whereas the rest of the system has mostly (there are a few other uses of ProxyObjects remaining) eliminated the use of the non-native get/set methods.
- removed use of `ProxyMixin` in the `settings` service by grabbing the attributes off the setting model after fetching and using `Object.defineProperty()` to add native getters/setters that pass through to the model's getters/setters. Ember's autotracking automatically works across the native getters/setters so we can then use the service as if it was any other native object
- updated all code to use `settings.{attrName}` directly for getting/setting instead of `.get()` and `.set()`
- removed use of observer in the `customViews` service because it was being set up before the native properties had been added on the settings service meaning autotracking wasn't able to set up properly
refs https://github.com/TryGhost/Ghost/issues/14101
Twitter/facebook URL validation doesn't follow our typical validation and was duplicated across multiple screens making the controllers unnecessarily complex.
- extracted url input fields and their validation into separate components
- uses tracked scratch values so that the input field values can reset to the saved value on save
- twitter/facebook URL inputs are different to our other inputs because invalid values won't prevent saving, instead they are reset to their previous value on save
- added `this.validate()` call after a successful save in `settings` service so the service and underlying model validations are both in sync (fixes validation error sticking around after saving with invalid twitter/facebook values that have been reset)
