Do not return bool for first_authenticate

[szszszsz]

To keep style consistent, do not return bool for first_authenticate, but instead throw exception on error.

Since this will break ABI, it should be done in the next major release.

https://github.com/Nitrokey/libnitrokey/blob/2e38681cd0b34e1ce36a6417445f3a7ca75f246c/libnitrokey/NitrokeyManager.h#L52