config: no longer singleton. it is passed to Wallet.__init__

The few other cases that used SimpleConfig.get_instance() now
either get passed a config instance, or they try to get a reference
to something else that has a reference to a config.
(see lnsweep, qt/qrcodewidget, qt/qrtextedit)

electrum/tests/test_util.py

@@ -3,10 +3,10 @@ from decimal import Decimal
 from electrum.util import (format_satoshis, format_fee_satoshis, parse_URI,
                            is_hash256_str, chunks, is_ip_address, list_enabled_bits)
 
-from . import SequentialTestCase
+from . import ElectrumTestCase
 
 
-class TestUtil(SequentialTestCase):
+class TestUtil(ElectrumTestCase):
 
     def test_format_satoshis(self):
         self.assertEqual("0.00001234", format_satoshis(1234))