Implementing HiPACE unit conversion definitions and some fixes

[delaossa]

Changes:

• Implement HiPACE unit conversion.
• Bug fixes in HiPACE implementation.
• Add support for new Osiris data.
• Define vector potential field A and add unit conversion.
• Redefine normalized vector potential a as dimensionless.
• Dimensionless fields won't be affected by unit conversion.

[AngelFP]

Well, I think this concludes it from my side, but let me know if you have any comments. And thanks again for the improvements!