Docs: Add autodoc for analytics, promotions, shipping apps

They were missing the autodoc documentation for views (abstract) and
abstract models.
Also added two docstrings to the views in the promotions app to have
them showing in the autodoc.
Docs: Discourage admin more

We currently mention it in internals/sandbox.rst. I've added a note to
the dashboard app (ref/apps/dashboard.rst), the sandbox/urls.py and
expanded on the feature explanation on index.rst.

Fixes #816
Drop footer links

The About link was a 404 in a default sandbox installation because it
relied on a flatpage being existent. The Top of the Page link is bad UI
design, see #819 for an explanation.

Fixes #819
Update and re-enable template timings panel

It has been considerably improved and doesn't cause any significant
performance hit anymore. Hence, it's been enabled by default again.

@maikhoepfel also took the opportunity to re-order the DDT panels.

Fixes #820
Fix typo in promotions dashboard view
Remove urlencode that was missed previously
Fix broken links with page promotions
Tidy promotions dashboard template
Show breadcrumbs on flatpages page
Minor basket template changes

- Add breadcrumbs to summary page
- Don't use button for normal link
Simplify tagline
Merge remote-tracking branch 'upstream/master'
reverted package order