message: Prepare changelog for v0.12.0-rc.5
diff: +Changes in [0.12.0-rc.5](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.0-rc.5) (2018-04-09)
  +===============================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.0-rc.4...v0.12.0-rc.5)
  +
  + * Added radio button to set group join policy
  + * Fix to prevent guests from accessing lab features
  + * Fix broken forgot password page
  + * Fix crash when joining a room after peeking
  +
  Changes in [0.12.0-rc.4](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.0-rc.4) (2018-03-22)
  ===============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.0-rc.3...v0.12.0-rc.4)
  