Initial import of crypto libs from SecureMicroMeshRouting

Pull request contains the extracted crypto libraries from Zacharias SecureMicroMesh Routing library with some changes:
- refactored the libraries to satisfy our conding conventions
- removed some interdependencies to make them usable stand-alone
- moved the sha256 implementation to fit the new structure in sys/crypto

The following crypto and hash libraries are now available:
- Triple-DES
- AES
- RC5
- SHA256
- SkipJack
- TwoFish

All of the added and the existing sha256 libs are now usable by including
```
USEMODULE += crypto_xxxx
```
into the project makefile and 
```
#include "crypto/xxxx.h"
```
in the source.