* fix(ui): remove opacity classes from transition enter and leave props
The flickering was caused by the opacity classes in the `leave` prop to take effect as the
transition ends; when the `leaveTo` prop classes are no longer applied, but the `leave` prop classes
are still applied.
* fix(ui): resolve transition issues for all components
1. Remove opacity classes from `enter` and `leave` props
2. Fix some class name typos
3. Remove transform classes since those are automatically applied as from TailwindCSS v3.0
4. Narrow down `transition` classes to only the properties being transitioned in Transition components
* feat(api): allow importing of only selected Plex users
* feat(frontend): modal for importing Plex users
* feat: add alert if 'Enable New Plex Sign-In' setting is enabled
* refactor: fetch all existing Plex users in a single DB query
Co-authored-by: Ryan Cohen <ryan@sct.dev>
