New dashboard (WIP)

This PR is only for discussion purposes, this must not be merged to `master` yet.

- Decide on `@import` load for future style guide  

```
@import
"dashboard/header",
"dashboard/tables";
```

or use an import per line?

```
@import "dashboard/header";
@import "dashboard/tables";
```

In any case we should use `@import` instead of require when possible, and explicitly require files. Using `require_tree` is no good.