Cleaning up yet more future tense goodness.

Add none/unassigned metadata to pages.

On sign-out Devise invalidates all remember me tokens. GitLab
now also invalidates all remember me tokens whenever any given
Active Session is revoked manually by a user.

Links to issues need to be update to use a hyphen,
this MR changes issue links in /doc/user

The URLs needs hyphens now, so did a find and
replace to add them.

Add removing old sessions

Add proper order of sessions

Add more precise specs

Add more precise specs

Remove obsolete code

Add changelog entry

Update specs to use constant instead of fixed numbers

Refactor accessing redis

Refactor active session cleanup

Refactor cleanup method

Add cr remarks

Remove new line

This changes any mention of gitlab-ce to gitlab-foss, and any mention of
gitlab-ee to just gitlab.

Each of these files were edited to ensure compliance
with the docs standard layout, as part of the SSOT epic.

In addition, some copy editing was done, to improve clarity,
and comply with the GitLab docs style guide.

Session ID is used as a parameter for the revoke session endpoint but it
should never be included in the HTML as an attacker could obtain it via
XSS.