Clean up and fix account adding

As per BIP44, 20 addresses are checked for transactions, not just the
first one.
Show the last account only if used or named.
If all accounts are used, prompt for password to create new one.

Fixes #1128

lib/account.py

@@ -75,6 +75,10 @@ class Account(object):
     def redeem_script(self, for_change, n):
         return None
 
+    def is_used(self, wallet):
+        addresses = self.get_addresses(False)
+        return any(wallet.address_is_old(a, -1) for a in addresses)
+
     def synchronize_sequence(self, wallet, for_change):
         limit = wallet.gap_limit_for_change if for_change else wallet.gap_limit
         while True:
@@ -94,36 +98,6 @@ class Account(object):
         self.synchronize_sequence(wallet, True)
 
 
-class PendingAccount(Account):
-    def __init__(self, v):
-        self.pending_address = v['address']
-        self.change_pubkeys = []
-        self.receiving_pubkeys = [ v['pubkey'] ]
-
-    def synchronize(self, wallet):
-        return
-
-    def get_addresses(self, is_change):
-        return [] if is_change else [self.pending_address]
-
-    def has_change(self):
-        return False
-
-    def dump(self):
-        return {'pending':True, 'address':self.pending_address, 'pubkey':self.receiving_pubkeys[0] }
-
-    def get_name(self, k):
-        return _('Pending account')
-
-    def get_master_pubkeys(self):
-        return []
-
-    def get_type(self):
-        return _('pending')
-
-    def get_xpubkeys(self, for_change, n):
-        return self.get_pubkeys(for_change, n)
-
 class ImportedAccount(Account):
     def __init__(self, d):
         self.keypairs = d['imported']
@@ -399,5 +373,3 @@ class Multisig_Account(BIP32_Account):
 
     def get_type(self):
         return _('Multisig %d of %d'%(self.m, len(self.xpub_list)))
-
-