CLI improved and extended

account
* get_account_history is more robust against empty rpc returns
steem
* add functions to store default vote weight and nodes
cli
* Same parameter as in steempy are used
* main parameter improved
* set improved
* addkey improved
* delkey added
* listkeys improved
* info improved and info about a block, an account, post and a public key added
Unit tests
* test_testnet improved
* test_cli adapted on changes