v2.3.0: - IPFS Support

  We now support storing and fetching ipfs-data directly in incubed. The incubed client always calculated the ipfs hash and verifies the requested data.
- full scrypt-support for decrypting keystore files using scrypt as kdf-function.
- refactored Java-API
- optimize client properties by using flags for properties.
- auto registry of verfiers. using the `client_init.h` will automaticly register all bundled verifiers. So no need to explicitly register them.
- Clean up of public header-files, which removes a lot of internal headers.
- Ensure Verification with at least one signer when updating the nodelist