Stable v2.10.7

• fix(firewall): background refreshes no longer replace the tables with a spinner
• fix(lint): US spelling in the slice-apply test
• fix(slices): resource limits reach the kernel, not just the unit file
• fix(lint): US spelling in the staging-path and security-i18n tests
• fix(wordpress): a staging clone can finally be saved — and stops leaving an orphan behind
• docs: fill the demo fixture with mail, certificates, staging and cache, and clear the demo's old leftovers
• fix(security-advisor): translate check titles and status, test every backend check ID
• docs: add a reproducible screenshot fixture for the demo instance
• docs: bring the manuals up to stable 2.10.5 and 2.10.6