[REF] dev_backend_reports: assets and less

[switch87]

Before this commit the section "Custom fonts" was outdated with adding assets in a view and use of less

After this commit the assets are added in the manifest file and the stylesheet is of filetype scss

[robodoo]

Pull request status dashboard.

[switch87]

@toaa-odoo @mart-e

[kmagusiak]

Could you rebase and solve conflicts? Otherwise the PR looks good.