Move error page rules, other error page cleanup

Styles needed only by error pages are moved into their own stylesheets,
some stylesheets are renamed, and some old-design support is removed.
add source_url tracking for newsletter signups
Use Memcache and clean up caching setup.

- remove django-cache-machine

- removed secondary cache alias again

- use Django's cached_property decorator instead of own

- updated constance's cache setting to last format

- django-memcached-hashring for consistent hashing (based on python-memcached)

Fixes #1780.
Moved charset and X-UA-Compatible meta element to the right place
small fix to use the bulletproof font face syntax
Merge pull request #1853 from jezdez/cache-cleanup

[DO NOT MERGE] Use Memcache and clean up caching setup.
Removing cycle and slideshow resources which aren't used
load Open Sans fonts from mozorg cdn
Reduce the number of database queries done by the Submission.get_flags method in the demos app.

Do some PEP8 work while I’m here.
Fixed a few import errors.
Merge pull request #1871 from icaaq/bug_958638_load_fonts_from_mozorg

load Open Sans fonts from mozorg cdn
Merge pull request #1872 from icaaq/bullet_proof_fontface_syntax

small fix to use the bulletproof font face syntax so IE9 wont get woff fonts
Merge pull request #1864 from icaaq/move_metadata

Bug 958238 - The X-UA-Compatible meta element is placed to late in the document
Merge pull request #1873 from darkwing/remove-slideshow-cycle

Removing cycle and slideshow resources which aren't used
Reformat modal JS, remove useless resources from demo popup
Remove init.js, move required functionality to relevant files
Merge pull request #1867 from darkwing/init-js

Remove init.js, move required functionality to relevant files
Merge pull request #1877 from darkwing/modal-control-js

Reformat modal JS, remove useless resources from demo popup
The 'No Comments' heading is scrunched together and shouldn't be
Merge pull request #1878 from darkwing/demo-comments-heading

The 'No Comments' heading is scrunched together and shouldn't be