Adding OTP-Java

[BastiaanJansen]

A library for generating one-time passwords which can be used for two-factor authentication.

Features:

• Generation of secrets
• Time-based one-time password (TOTP, RFC 6238) generation based on current time, specific time, OTPAuth URI and more for different HMAC algorithms.
• HMAC-based one-time password (HOTP, RFC 4226) generation based on counter and OTPAuth URI.
• Verification of one-time passwords
• Generation of OTP Auth URI's