* Consolidate crypto functionality in `ethcore-crypto`.
- Move `ecdh`/`ecies` modules to `ethkey`.
- Refactor `ethcore-crypto` to use file per module.
- Replace `subtle` with `ethcore_crypto::is_equal`.
- Add `aes_gcm` module to `ethcore-crypto`.
* Rename `aes::{encrypt,decrypt,decrypt_cbc}` ...
... to `aes::{encrypt_128_ctr,decrypt_128_ctr,decrypt_128_cbc}`.
* whisper skeleton
* basic message store
* rallying and message logic
* pass host info to network protocol handlers
* choose who starts rally based on node key
* module reshuffling
* mining messages
* prune messages by low PoW until below size target
* associated error type for ethkey generators and `OsRng` generator
* beginnings of RPC
* generic message handler for whisper
* reshuffle code order
* standard payload encoding and decoding
* basic crypto
* minor restructuring of net code
* implement shh_post
* merge?
* implement filters
* rand trait for hash types
* filter RPCs for whisper
* symmetric encryption of payload
* pub-sub
* filter tests
* use only secure random IDs
* attach arbitrary protocols to network
* basic integration of whisper into Parity
* eagerly prune low PoW entries
* broadcast messages with salted topics
* node info RPC
* fix import
* fix leading zeros calculation
* address minor grumbles
