Changed all Cipher and Signature method variables to object variables
Fixed Javadoc
Changed all non-private CryptoUtils methods to synchronized
CryptoUtils now throws RuntimeExceptions for fatal initialization errors
Refactored exception handling in CryptoUtils.
Exceptions which are the result of invalid input values are now thrown
Changed Mac method variable to object variable
Merge pull request #161 from L-Henke/cryptoUtilsRefactor

CryptoUtils refactorization
Added DropURL class
Removed checks and tests of drop url syntax form DropServer

These tests are specific to URL fully qualifying a drop instead
of a drop server.
Therefore, the checks and tests have been moved to new drop url class.
Adapted code to use DropURL class