Clean up block explorer handling. Add menu item to go to block explorer for an address.

Block explorer code is data-driven now.
Put block explorer defaulting in one place.
Fix URLs for insight.is and blockr.io.
Add tradeblock.com explorer.
Add menu item to view address on block explorer provided only one is selected.

gui/qt/main_window.py

@@ -18,6 +18,7 @@
 
 import sys, time, re, threading
 from electrum.i18n import _, set_language
+from electrum.util import block_explorer, block_explorer_info, block_explorer_URL
 from electrum.util import print_error, print_msg
 import os.path, json, ast, traceback
 import shutil
@@ -1402,6 +1403,9 @@ class ElectrumWindow(QMainWindow):
                 menu.addAction(_("Encrypt/decrypt message"), lambda: self.encrypt_message(addr))
             if self.wallet.is_imported(addr):
                 menu.addAction(_("Remove from wallet"), lambda: self.delete_imported_key(addr))
+            addr_URL = block_explorer_URL(self.config, 'addr', addr)
+            if addr_URL:
+                menu.addAction(_("View on block explorer"), lambda: webbrowser.open(addr_URL))
 
         if any(addr not in self.wallet.frozen_addresses for addr in addrs):
             menu.addAction(_("Freeze"), lambda: self.set_addrs_frozen(addrs, True))
@@ -2562,11 +2566,11 @@ class ElectrumWindow(QMainWindow):
         unit_combo.currentIndexChanged.connect(on_unit)
         widgets.append((unit_label, unit_combo, unit_help))
 
-        block_explorers = ['Blockchain.info', 'Blockr.io', 'Insight.is', "Blocktrail.com"]
+        block_explorers = sorted(block_explorer_info.keys())
         block_ex_label = QLabel(_('Online Block Explorer') + ':')
         block_ex_combo = QComboBox()
         block_ex_combo.addItems(block_explorers)
-        block_ex_combo.setCurrentIndex(block_explorers.index(self.config.get('block_explorer', 'Blockchain.info')))
+        block_ex_combo.setCurrentIndex(block_explorers.index(block_explorer(self.config)))
         block_ex_help = HelpButton(_('Choose which online block explorer to use for functions that open a web browser'))
         def on_be(x):
             be_result = block_explorers[block_ex_combo.currentIndex()]