closesTryGhost/Ghost#8107
- replaces all icons in Ghost-Admin with SVGs by using our new helper {{inline-svg}}.
- removes all ghosticon fonts.
This is the second and final batch of the refactor.
closes https://github.com/TryGhost/Ghost/issues/8269
- swaps the usage of our custom `gh-dropdown` component in the user menu dropdown for the `ember-wormhole` based `ember-basic-dropdown` that is used elsewhere in the app and will fully replace `gh-dropdown` in the future
- adds `gh-basic-dropdown` component that extends from `ember-basic-dropdown` and hooks into our `dropdown` service so that we can programatically close dropdowns from disparate areas of the app
- modifies the `body-event-listener` mixin to pass the click event through to it's consumers
- modifies the `bodyClick` handler in the `dropdown` service to check if the click actually originated from an ember-basic-dropdown element - this body click handler will go away once we've fully switched to `gh-basic-dropdown`
- adds `ember-native-dom-helpers` to provide consistency between acceptance and integration tests (this is the start of another refactor, eventually this addon will disappear as part of ember's [grand testing unification project](https://github.com/rwjblue/rfcs/blob/42/text/0000-grand-testing-unification.md))
- Lighter dropdown shadow
- Removed display:flex from .btn because safari can't handle it on <button> elements, where it will immediately set all text-alignment to "left" with no way to change. I haven't been able to find any regressions for this change so far. Can't remember why buttons were supposed to be flexbox anyway. Maybe for icon alignment within buttons, but I can't find any such examples within the app.
- Safari thinks that user-select: all; means a single click should SELECT ALL THE THINGS. Removed/replaced with user-select: text; which makes it behave like Chrome; click and drag to select.
- Increased hit area for "?" button
- Removed :active style for post-edit button on content management screen, adjusted position
- Increased contrast on tag description, tag count, and view blog links
See #5652
