* Refactor editor css, fix editor button highlight
- Avoid using webview.css
- Move more buttons css into button_mixins
* Fix DropdownItem appearance
* Fix the visuals of tags
* Make dropdown font slightly smaller
* Give SelectOption a background color
* Move some css from deck-options-base to CardStateCustomizer
* Avoid using core.scss for CardStats
* Avoid using sass/core in congrats package
* Inline core.scss into webview.scss
* Include fusion-vars for base.scss
* need to keep core.scss around for now (dae)
- Rework V2 upgrade so that it no longer resets cards in learning,
or empties filtered decks.
- V1 users will receive a message at the top of the deck list
encouraging them to upgrade, and they can upgrade directly from that
screen.
- The setting in the preferences screen has been removed, so users
will need to use an older Anki version if they wish to switch back to
V1.
- Prevent V2 exports with scheduling from being importable into a V1
collection - the code was previously allowing this when it shouldn't
have been.
- New collections still default to v1 at the moment.
Also add helper to get map of decks and deck configs, as there were
a few places in the codebase where that was required.
