Added signature to encrypted messages.
Changed visibilities of methods in CryptoUtils.
Added log messages for (currently) unhandled exceptions.
Fixed usage of wrong RSAPrivateKey in CryptoUtils rsaSign()
Fixed sub-key signing. Changed method named in CryptoUtils
Fixed CryptoUtils rsa sign fix again
Changed CryptoUtils logger to final static
Merge pull request #59 from L-Henke/cryptoImprovement

Added signature to encrypted messages and CryptoUtils improvement.
Added Bouncy Castle cryptographic provider to build.gradle
Switched cryptographic provider to Bouncy Castle
Switched RSA signing algorithm to RSASSA-PSS
Merge pull request #63 from L-Henke/bouncyCastle

Added Bouncy Castle cryptographic provider to build.gradle
Changed rsaSign() parameter name from 'message' to 'data' to avoid confusion
Changed rsaSign() Javadoc description.
Renamed encryptHybrid() to encryptHybridAndSign() and
decryptHybrid() to decryptHybridAndValidateSignature() because encryption
and signing are indepented operations. This should be expressed by the
method name.
Merge pull request #62 from L-Henke/cryptoImprovement

Changed rsaSign() parameter name from 'message' to 'data'
started implementing of drop api
api encryption part done