Fix apache missing module diagnostics (fixes #390)

Treat 'apachectl'/'server-status URL loading' failing differently from 'missing
modules'. For the latter, show a list of required/missing apache modules so
sysadmin can load the right modules. For the former, show hints on how to solve
these problems.

Also fixed an CSS issue that went wrong while refactoring (diag_no was
renamed to diag_fail, but one was skipped when converting this, because this
was an exception)
Fix bug: diagnostics checked wrong email address

Instead of testing smtp_from, it tested commit_email_from. Likely the result
of a copy+paste.
Show more values in Diagnostics (refs #354)

Also fix some formatting.
Added more smtp_* options that I missed before (refs #391)
Updated changes to prepare for 2.2.0 release.
Released 2.2.0

Removed the preliminary release 2.1.3 and bumped the version to 2.2.0
because many changes were made since the previous release.
Add check for up-to-date versions (refs #387)

There is already a version in submin, but it is not kept up-to-date.
The Debian build package now checks if the debian/changelog version is
the same as the version in submin/__init__.py
Make submin version up-to-date (refs #387)
Show version in web-ui (refs #387)

Add SUBMIN_VERSION to template automatically. Show version in different places:
 * the login page,
 * the sidebar (hover over 'Submin' to see the version as title-text),
 * the intro page (only seen by admins).
Show version in submin2-admin (fixes #387)