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.

lib/util.py

@@ -188,6 +188,34 @@ def age(from_date, since_date = None, target_tz=None, include_seconds=False):
     else:
         return "over %d years ago" % (round(distance_in_minutes / 525600))
 
+block_explorer_info = {
+    'Blockchain.info': ('https://blockchain.info',
+                        {'tx': 'tx', 'addr': 'address'}),
+    'Blockr.io': ('https://btc.blockr.io',
+                        {'tx': 'tx/info', 'addr': 'address/info'}),
+    'Insight.is': ('https://insight.bitpay.com',
+                        {'tx': 'tx', 'addr': 'address'}),
+    'Blocktrail.com': ('https://www.blocktrail.com/BTC',
+                        {'tx': 'tx', 'addr': 'address'}),
+    'TradeBlock.com': ('https://tradeblock.com/blockchain',
+                        {'tx': 'tx', 'addr': 'address'}),
+}
+
+def block_explorer(config):
+    return config.get('block_explorer', 'Blockchain.info')
+
+def block_explorer_tuple(config):
+    return block_explorer_info.get(block_explorer(config))
+
+def block_explorer_URL(config, kind, item):
+    be_tuple = block_explorer_tuple(config)
+    if not be_tuple:
+        return
+    kind_str = be_tuple[1].get(kind)
+    if not kind_str:
+        return
+    url_parts = [be_tuple[0], kind_str, item]
+    return "/".join(url_parts)
 
 # URL decode
 #_ud = re.compile('%([0-9a-hA-H]{2})', re.MULTILINE)