API throttling

[facundoolano]

• Prevent the same user to send a lot of requests any short amount of time.
• Specially, prevent a same ip registering lots of users
• Consider to remove the ad hoc throttling of the reset password and send confirmation email endpoints.

[facundoolano]

http://api.stackexchange.com/docs/throttle http://www.django-rest-framework.org/api-guide/throttling/#throttling https://github.com/Gromina/raterlimiter