The xorm `Sync2` has already been deprecated in favor of `Sync`,
so let's do the same inside the Gitea codebase.
Command used to replace everything:
```sh
for i in $(ag Sync2 --files-with-matches); do vim $i -c ':%sno/Sync2/Sync/g' -c ':wq'; done
```
Change all license headers to comply with REUSE specification.
Fix#16132
Co-authored-by: flynnnnnnnnnn <flynnnnnnnnnn@github>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>
* add migration and basic UI for changing a user's theme
* update user themem
* use right text on button
* load theme based on users' selection
* load theme based on users' selection in pwa too
* update sample config
* delete older theme loading
* implement AfterLoad to set users' theme properly
* set up default theme when creating a user. This uses the installation wide theme
* use flash messages for error
* set default theme when creating a user from the cli
* fix @lunny review
delvh
flynnnnnnnnnn
Lunny Xiao
Lanre Adelowo