Handle bigger OTP secrets up to 40 bytes, 320 bits

This will support AWS-length secrets - 40 bytes Fixes #22

Tested using libnitrokey tests under Ubuntu 16.10 test_report_08.txt

Summary:

added new command for sending OTP data
removed tables with fixed OTP slots offsets (replaced with function)
casting slots storage and command packets to structs for easier data manipulation
allowing for setting any maximum OTP secret size (with a cost of lower count of OTP slots over some size)
handling 3rd HOTP slot for requesting code by double-pressing special key (+code cleanup)
removed unused code and comments

Nitrokey / nitrokey-pro-firmware