Added the possibility to define a default account

New dialog created : PasswordDialogAsker
Needs to be passed throught the Widgets managing the current account

Renaming actions in the member tab
Added a BlockchainInspector thread to check for new blocs and refresh the UI

Fx bug in wot if multiple certifications
Don't refuse certification in wot if one already exists

Removed old files

Fixed a bug when an inputs would be removed from available ones even if the transaction is refused
Added icons
Display community nodes again
Save community nodes and load them when acccessing a community object

Refactor wot to better handle node/arc metadata

Signing on the way. There is a bug becuse of ucoin API using keyword "self", and it's conflicting with python self keyword.

Wallet content now show available sources, while Transactions sent and received will display latest transactions sent and received

This reverts commit ebbbc390.

This reverts commit 2617284d.

Wont run because we have to port Pynacl code to libnacl