Fix bug 1008828: Show correct locale/slug in page move error.

The root of the problem was a child page move failing after the
child's locale/slug had already been changed in-memory; in that case
the new locale/slug would end up in the error message instead of the
original.

Now the original locale/slug get stashed away prior to attempting the
child move, and if the child move fails they get inserted in the error
message to ensure the error points to the correct URL.
Remove all compat-* functions in Stylus

The compat-* functions were used to override styles from the old design.
The functions used !important to do this. By removing the functions and
the associated use of !important, our stylesheets will be more
maintainable and reliable. This also reduces the size of compiled CSS by
2.04KB.

Some bugs were fixed just by removing these functions. At the same time,
some bugs were revealed by removing these functions. (For example,
errors related to selector specificity suddenly manifested as
user-facing bugs when !important was removed.)

Newly-manifesting bugs like these were searched for and corrected, but
it is possible that some remain. If we find any more, we can correct
them with later commits.
Reverting quick links change to they work with icons
Render document URLs with the already defined Document.get_absolute_url method instead of inline.
fix bug #1002371 - don't lose the query parameters when switching languages.
Ensure search top has proper background
Massive minification of all media-dir images
Use placeholder selectors wherever possible

The classes .review-base and .dev-program-pad have been updated to
placeholder selectors because, although they are extended, they do not
appear in markup. This saves 62 bytes of compiled CSS.
fix bug 865863 - remove duplicated styles
Merged ModelBase from devmo and sumo apps and get rid of cache machine.

This is an important step to have a leaner caching setup.
Added new "memcache" caching backend to be used by Jinja2 and constance.

Removed settings_local.py based CACHES setting in favor of settings.py.
This requires an update of all local_settings.py in use!
Move PageMoveError into exceptions module.
Extended render_stale_documents task to use a task group for its subtasks.

That means we can set a lock at the start of the task and destroy it again once the whole bunch of tasks have finished.
Added a MemcacheLock utility.
Use memcache cache backend for the rebuild task.