Release/beta rc2

### New PIConGPU Release: *Beta RC2*

Please refer to the [ChangeLog](https://github.com/ax3l/picongpu/blob/e58015211e2e6820d0bf1043b1b760d8a6e1cae7/CHANGELOG.md#open-beta-rc2) for detailed information.

It includes hints on how to update your ```.param``` files and which new features/fixes are shipped with that release of *PIConGPU*.