Added new PRNGs

Added a couple of new secure Pseudo Random Number Generators:
* *SHA1-PRNG*: a hash-based RNG
* *CTR-PRNG*: a Blockcipher in counter-mode (*AES*)
* *Stream-PRNG*: the keystream of a Streamcipher (with different algorithm options)
* (Since Java's *Random* is neither deterministic nor secure, it has been removed)

Since there are no good Streamciphers implemented in the default Java-Crypto-API, it was necessary to add *bouncycastle* to the project dependencies.

A little unit-test that compares the performance of the different RNGs has also been added. (Result: *StreamPRNG* is about 6x as fast as the Java default *SecureRandom* hash-based implementation)