Market
* _weighted_average, btc_usd_ticker, steem_btc_ticker and steem_usd_implied added
Witness
* get_votes_sum added to witnesses object
Graphenerpc
* fix handling of WebSocketConnectionClosedException
CLI
* witnessfeed: uses the new market ticker to calculate the current steem_usd price as base. When using support-peg the sbd_usd price is calculated from the internal ticker and used for quote.
* Witness: shows the rank and active rank (when it is below 250). virtual_time_to_block_num is calculated from num_scheduled_witnesses, VIRTUAL_SCHEDULE_LAP_LENGTH2 and vote_sum. This is then used to estimate the next block producing time.
* witnesses uses a proxy now, when set.

blockchain.awaitTxConfirmation() fix timeout

actually wait `limit` blocks before raising an exception

CLI
* add witnessenable, witnessdisable, witnessfeed and witness
Vote
fix reputation

CLI
* updatenodes added, this command can be used to update the nodes list
NodeList
* update_nodes added, this command reads the metadata from fullnodeupdate, which contain newest nodes information
* add option wss and https fo get_nodes
Unit tests
* use updatenodes in all tests

Account features + some fixes and refactorings

* use utils.addTzInfo()
* use constants.STEEM_1/100_PERCENT

* Raise OfflineHasNoRPCException in offline mode, when rpc should be used
* Unit test for beneficiaries
* Fixes bug for python 2.7 in blockchain

Fix beneficiaries handling in Comment_options

Fixes #20