Use stock BouncyCastle, remove embedded libs, convert to Maven

[ibauersachs]

Closes #4, closes #5

I can try to create multiple smaller pull requests if necessary, but that will be difficult.

Modifications:

• BigIntegerCrypto removed: incompatible with BouncyCastle
• Embedded BouncyCastle removed: code duplication just for BigIntCrypto
• Embedded Curve25519 removed: in BouncyCastle
• Mavenization: can create an OSGi bundle automatically, doesn't need embedded jars
• Eclipse files removed: can be created from Maven
• Fortuna: embedded from bccontrib to avoid dependency. Uses a wrapper now and allows setting a different random source externally
• License: all GPL-3+ with classpath exception now

[champtar]

Hi @ibauersachs,

Haven't read your patch bomb :)
Are you periodically reseeding Fortuna periodically?

[ibauersachs]

@champtar No, but it's now possible to externally set a different SecureRandom implementation (before the new ZrtpSecureRandom is first accessed).

[ibauersachs]

@champtar Oh, and patch bomb: yes, but if you skip all the deleted files it actually isn't much.