Add CSRF tokens for API actions

[mattdowdell]

Pretty much all API actions should use CSRF token based authentication to improve security.

• Implement CSRF token functionality (3fe888a).
• Implement token usage into each controller/action.
  • V1::UsersController (a497430)
  • V1::GroupsController (742e3cf)
  • V1::DevicesController
  • V1::Admin::DevicesController
• Document token usage on wiki
  • Users
  • Groups
  • Devices
  • Devices (Staff)