Refuse to start if no mpks or addrs are configured

Lots of newbs dont configure any master public keys or
addresses at all, this error message will be helpful to
them.

electrumpersonalserver/server/common.py

@@ -523,6 +523,12 @@ def get_scriptpubkeys_to_monitor(rpc, config):
         watch_only_addresses_to_import = (watch_only_addresses -
             imported_addresses)
 
+    if len(deterministic_wallets) == 0 and len(watch_only_addresses) == 0:
+        logger.error("No master public keys or watch-only addresses have " +
+            "been configured at all. Exiting..")
+        #import = true and no addresses means exit
+        return (True, [], None)
+
     #if addresses need to be imported then return them
     if import_needed:
         addresses_to_import = [hashes.script_to_address(spk, rpc)
@@ -693,6 +699,9 @@ def main():
     import_needed, relevant_spks_addrs, deterministic_wallets = \
         get_scriptpubkeys_to_monitor(rpc, config)
     if import_needed:
+        if len(relevant_spks_addrs) == 0:
+            #import = true and no addresses means exit
+            return
         transactionmonitor.import_addresses(rpc, relevant_spks_addrs)
         logger.info("Done.\nIf recovering a wallet which already has existing" +
             " transactions, then\nrun the rescan script. If you're confident" +