Several improvements and fixes

Account
* Example added for transfer
Nodelist
* Doc added
Steem
* steemconnect integration improved and use_sc2 added
* Docu improved
SteemConnect
* compatible with py2.7
* several improvements
* Examles added
Transactionbuilder
* Integration of steemconnect improved
Wallet
* fix bug
SteemNodeRPC
* fix old and removed parameter n_urls
Doc
* Fix bug in tutorial page