AsciiChart added and charts added to cli

AsciiChart
* new ascii curve plot class created
* width and height can defined and plot() prints an ascii string, which can be interpreted as plot
CLI
* keyring functionallity added
* walletinfo shows if UNLOCK env is set, keyring is installed and if it possible to unlock the wallet (--test-unlock)
* ticker shows a table with the latest market prices
* pricehistory plots the history of the last 3 days together with the median price
* tradehistory shows the STEEM/SBD market price history
* orderbook has now a working chart option
* The sum of SBD and STEEM for open orders was added
Unit test
* tests for new cli function were added