account.history_reverse() fix for TypeError

Fixes #13

Account
* datetime.date is also supported
CLI
* curation improved
Comment
* doc improved
Transactionbuilder
* doc fixed
* owner key is taken, when no other permission is proved
utils
* datetime.date supported
Wallet
*   raise MissingKeyError when a wrong key is given by Steem(keys=[])
Unit tests
* several unit tests has to be changed as now it is really tested if a given wif belongs to the account or not.

NodeList
* replaces get_node_list from utils.py
* is a list and contains all nodes as dict
* get_nodes() returns the url in a list
Utils
* get_node_list removed
Unit Tests and Examples adapted to the changes

Wallet
* getKeysForAccount added
* getOwnerKeysForAccount, getActiveKeysForAccount, getPostingKeysForAccount added
beemapi
* WorkingNodeMissing is raised when no working node could be found
GrapheneRPC
* cycle([urls]) is replaced by the nodes class
Nodes
* Node handling and management of url and error_counts is performed by the nodes class
* sleep_and_check_retries is moved to the nodes class
* Websocket, steemnodrpc were adpapted to the changes
Unit tests
* new tests for the nodes class
* tests adapted for websocket and rpcutils

CLI
* speed up votes and added export to text file
* curation can be used to export all pending curation rewards of one account

Scheduled weekly dependency update for week 20

beembase\objects
* Amount improve handling of new appbase Amount format
beembase\operations
* Account_witness_proxy added
* Custom added
* Custom_binary added
* Prove_authority added
* Limit_order_create2 added
* Request_account_recovery added
* Recover_account added
* Escrow_transfer added
* Escrow_dispute added
* Escrow_release added
* Escrow_approve added
* Decline_voting_rights added
Unit tests
* add test_order_create2, test_witness_proxy, test_custom, test_request_account_recovery,  test_recover_account, test_escrow_transfer, test_escrow_dispute, test_escrow_release, test_escrow_approve, test_decline_voting_rights, test_delegate_vesting_shares, test_account_create_with_delegation added

Readme for last release adapted

Set use_condenser to True
Add unit test for hash_op

CLI
* sbd-to-steem option added to ticker and tradehistory
* curation: account and limit option added
* High. vote and Highest curation added to curation
* Some bug fixes

Tutorial about Transactionbuilder fixed

wait_for_and_get_block refactoring

* remove redundant Block() calls
* don't wait `block_interval` seconds before raising the exception

Blockchain
* raw_ops added to stream, when set to True stream() produces the same output as the old Blockchain.ops()
Unit tests
* Add unit tests for testing raw_ops