Scheduled weekly dependency update for week 17

* Add hive node
* update_account function added to blockchaininstance
* normalize added to PasswordKey, so that a Brainkey can be set as PasswordKey
* Fixed vote percentage calculation when post rshares is negative
* new beempy command changekeys
* beempy keygen can be used to generate account keys from a given password and is able to generate new passwords

Add witness proxy management functions

Scheduled weekly dependency update for week 16

* Rshares, vote percentage and SBD/HBD calculation has been fixed for votes
* post_rshares parameter added to all vote calculations

Rename SteemWebsocket to NodeWebsocket and SteemNodeRPC to NodeRPC

* steem object in all classes is replaced by blockchain
* Hive and Steem are now BlockChainInstance classes
* Each class has now blockchain_instance parameter (steem_instance is stil available)
* shared_blockchain_instance and set_shared_blockchain_instance can be used for Hive() and Steem() instances
* token_symbol, backed_token_symbol and vest_token_symbol

Snapshot update