Depend on openPMD-api

[ax3l]

Hi,

can you please replace the h5py dependency with openPMD-api? Here are its docs.

This would bring the following benefits:

• support of all backends, such as .h5, .bp (important for daily PIConGPU), .json, ...
• extended testing of our new library by an in-house user (with easy support from our side)
• easier forward-updates to new versions of the openPMD-standard in the future (less maintenance here)
• in the future, easier updateability for upcoming staging ("data streaming") methods by @franzpoeschel

[ax3l]

Implemented, thanks a lot! :)