Wiki and Product APIs. Added for Yaocho.

This squashes the following commits:

ae0ff3e Document viewing and browsing API.
4dc7d5f WIP on products API.
a3f7c3a Changes for yaocho topic browser.
e623a8b API Accept-Language
a201ddf Test and fix LocaleNegotiationMixin.
1c041fa Filter out non-useful articles.
b62bc25 test language negotiater
9b3ab92 Test Product.path
6419ec2 Localize topic names.
6f96637 idk, something.
9b7988a Feedback
41b0adc More feedback.
e25cb56 Versioned api and bool() querystrings.

Document viewing and browsing API.

WIP on products API.

Changes for yaocho topic browser.

API Accept-Language

Test and fix LocaleNegotiationMixin.

Filter out non-useful articles.

test language negotiater

Test Product.path

Localize topic names.

idk, something.

Feedback

More feedback.

In particular, less funky queryset manipulation and more docstrings.

Versioned api and bool() querystrings.