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.
no issue
- removes `gh-select-native` component as ember-one-way-control's `one-way-select` component offers the same one-way-binding but also allows element attributes to be set
refs https://github.com/TryGhost/Ghost/pull/7142, https://github.com/TryGhost/Ghost/pull/7143
- moves timezone selection template and logic into a component
- detect if the current `activeTimezone` is not in our pre-defined list of timezones, if it isn't:
- add a line indicating that there has been an override with the current `activeTimezone` value
- add a blank option to the timezone select list
