* First take on subsetting svg icons
* FontAwesome 5 svg subset WIP
* Include icons from plugins/badges into svg sprite subset
* add svg icon support to themes
* Add spec for SvgSprite
* Misc. SVG icon fixes
* Use FA5 svgs in local-dates plugin
* CSS adjustments, fix SVG icons in group flair
* Use SVG icons in poll plugin
* Add SVG icons to /wizard
* Phase 0 for user-selectable theme components
- Drops `key` column from the `themes` table
- Drops `theme_key` column from the `user_options` table
- Adds `theme_ids` (array of ints default []) column to the `user_options` table and migrates data from `theme_key` to the new column.
- Removes the `default_theme_key` site setting and adds `default_theme_id` instead.
- Replaces `theme_key` cookie with a new one called `theme_ids`
- no longer need Theme.settings_for_client
Adds a "Step 0" to the wizard if the site has no admin accounts where
the user is prompted to finish setting up their admin account from the
list of acceptable email addresses.
Once confirmed, the wizard begins.
