Nitrokey Storage-only version

[szszszsz]

Divide implementation in such a way, that would allow to produce library containing only Nitrokey Storage features handling.
Target is to decrease the final binary size for the Heads use.

[szszszsz]

WIP work in: https://github.com/Nitrokey/libnitrokey/compare/184-storage-only

[szszszsz]

cc @daringer