Expose OTP and PWS properties (slot counts, limits)

[robinkrahl]

To allow applications to validate user input before sending it to the device (see d-e-s-o/nitrocli#161), it would be nice to be able to access some OTP- and PWS-related properties using libnitrokey:

• TOTP and HOTP slot counts
• PWS slot count
• maximum OTP name and secret length
• maximum PWS name, login and password length

As far as I know, these values are the same for all supported devices, but are likely to change in the future. Therefore I suggest to not have them as constants but to add functions that return the value for the currently connected device instead.

If you don’t object, I’ll prepare a PR soon.

[szszszsz]

Good idea! Please proceed.