When a non sqlite database is used, loading the admin interface fails
because the backup button is not generated.
This PR is solves it by checking if the elements are valid.
Also made some other changes and fixed some eslint errors.
Showing `_post` errors is better now.
Update jquery to latest version.
Fixes #3166
- Removed `unsafe-inline` for javascript from CSP.
The admin interface now uses files instead of inline javascript.
- Modified javascript to work not being inline.
- Run eslint over javascript and fixed some items.
- Added a `to_json` Handlebars helper.
Used at the diagnostics page.
- Changed `AdminTemplateData` struct to be smaller.
The `config` was always added, but only used at one page.
Same goes for `can_backup` and `version`.
- Also inlined CSS.
We can't remove the `unsafe-inline` from css, because that seems to
break the web-vault currently. That might need some further checks.
But for now the 404 page and all the admin pages are clear of inline scripts and styles.
