no issue
- the upcoming Module Unification re-organisation in Ember will no longer support nested components
- this PR pre-emptively moves our usage of nested components into a flat file structure
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.
refs #5798, closes#5018
- adds new `gh-fullscreen-modal` component - modals are now specified in-context so that they can have deeper interaction with their surrounding components/controller/route, i.e. a modal component can be a thin confirm/deny wrapper over the underlying controller action keeping all context-sensitive logic in one place
- adds spin-buttons to all modals with async behaviour
- adds/improves behaviour of inline-validation in modals
- improves re-authenticate modal to properly handle validation and authentication errors