Fix contact editing.

This fixes some bugs in contact editing:

- a changed address is now checked for validity. Shows
  error if invalid and restores prior value
- the changes are saved, before they were dropped
- adding a new contact switches to the contacts tab,
  it used to switch to the address tab

As an enhancement, the contact name, as well as its address,
can be edited and updated.

Finally, the platform edit key can also be used to edit,
in adition to double-clicking.  This is typically the F2 key.

gui/qt/main_window.py

@@ -1507,7 +1507,8 @@ class ElectrumWindow(QMainWindow):
         return self.create_list_tab(l)
 
     def create_contacts_tab(self):
-        l = MyTreeWidget(self, self.create_contact_menu, [_('Key'), _('Value'), _('Type')], 1)
+        l = MyTreeWidget(self, self.create_contact_menu, [_('Name'), _('Address'), _('Type')], 1, [0, 1])
+        l.item_edited = self.contact_edited
         self.contacts_list = l
         return self.create_list_tab(l)
 
@@ -1645,6 +1646,22 @@ class ElectrumWindow(QMainWindow):
         self.payto_e.setText(addr)
         self.amount_e.setFocus()
 
+    def contact_edited(self, item, column, prior):
+        if column == 0:  # Remove old contact if renamed
+            self.contacts.pop(prior)
+        self.set_contact(unicode(item.text(0)), unicode(item.text(1)))
+
+    def set_contact(self, label, address):
+        if not is_valid(address):
+            QMessageBox.warning(self, _('Error'), _('Invalid Address'), _('OK'))
+            self.update_contacts_tab()  # Displays original unchanged value
+            return False
+        self.contacts[label] = ('address', address)
+        self.update_contacts_tab()
+        self.update_history_tab()
+        self.update_completions()
+        return True
+
     def delete_contact(self, x):
         if not self.question(_("Do you want to remove")+" %s "%x +_("from your list of contacts?")):
             return
@@ -1936,19 +1953,8 @@ class ElectrumWindow(QMainWindow):
         if not d.exec_():
             return
 
-        address = str(line1.text())
-        label = unicode(line2.text())
-
-        if not is_valid(address):
-            QMessageBox.warning(self, _('Error'), _('Invalid Address'), _('OK'))
-            return
-
-        self.contacts[label] = ('address', address)
-
-        self.update_contacts_tab()
-        self.update_history_tab()
-        self.update_completions()
-        self.tabs.setCurrentIndex(3)
+        if self.set_contact(unicode(line2.text()), str(line1.text())):
+            self.tabs.setCurrentIndex(4)
 
 
     @protected