* WIP: detect private browsing and safari blocked cookies
* just check for indexeddb
* just check for indexeddb
* change warning text
* change text
* change text again
* change text again
fixes#444
The point of this PR is to make it easier to implement scrollbars (#683).
With this PR, the themes move from a body tag-based system (e.g. `body.theme-scarlet`) to a system where they simply declare global CSS and we use CSS specificity order to give us the right theme.