Integrate eth_accounts and eth_transact to use new account manager

* Add from to eth_transact / xeth.Transact and add static pass in lieu
  of integrating with native Mist window for user passphrase entry
* Make eth_accounts return AccountManager.Accounts()
* Add a Generate Key menu item in Mist

cmd/mist/ui_lib.go

@@ -171,6 +171,7 @@ func (self *UiLib) Transact(params map[string]interface{}) (string, error) {
 	object := mapToTxParams(params)
 
 	return self.XEth.Transact(
+		object["from"],
 		object["to"],
 		object["value"],
 		object["gas"],