closes https://github.com/tryghost/ghost/issues/10088
* added `updateDocumentTitle` action to base route and replace usage of `.send('collectTitleTokens, [])`
* added `.titleToken()` method to editor route to add post title to document title
* called `.send('updateDocumentTitle')` after saving post title in editor controller to keep document title in sync
* updated editor controller test for latest ember-mocha and ember-test-helpers
refs https://github.com/TryGhost/Ghost/issues/9314
* added save button for contributor
* hide tag filter & redirect to posts.index if post is published
* update editor controller test to need session service
requires https://github.com/TryGhost/Ghost/pull/9277
- added a `koenigEditor` feature flag
- modified the feature service to accept a `developer` boolean on the options object passed into the internal `feature` method, if `true` the feature flag won't be enabled unless the `enableDeveloperExperiments` config option is also enabled
- added "developer feature testing" section in labs that's only visible if `enableDeveloperExperiments` config flag is enabled
- added koenig editor toggle to the developer section in labs
- enabled a switch between the markdown and koenig editors
- modified the default value of the `mobiledoc` attr in the Post model to be a blank mobiledoc or blank markdown mobiledoc depending on the feature flag
- modified the `autofocus` switch in editor controller's `setPost` method so that it is always switched, even for new->edit where the post model isn't swapped
- added a compatibility check to the editor controller's `setPost` method that shows an alert and force enables the koenig editor if the koenig flag is not enabled and the opened post is not compatible with the markdown editor
- fixed various issues that have appeared due to the old koenig alpha becoming out of sync with master
closesTryGhost/Ghost#8287closesTryGhost/Ghost#8750
- moved all editor model functionality into the new `editor` route+controller
- moved editor template from `editor/edit.hbs` to `editor.hbs`
- refactored `editor` controller and the `editor.new`/`editor.edit` routes to work with a persistent editor rather than a teardown/re-render when transitioning from new->edit
- fixed issue in `{{gh-markdown-editor}}` for `autofocus` behaviour when the component isn't re-rendered
- fixed issue in `{{gh-simplemde}}` that was causing multiple updates to the `value` property when a new value is passed in to the component
- added `{{gh-scheduled-post-countdown}}` component to lower the noise in the editor controller
- removed editor route/controller mixins
- removed the `editor.edit` and `editor.new` controllers
