Restructure invoices and requests (WIP)

- Terminology: use 'invoices' for outgoing payments, 'requests' for incoming payments
 - At the GUI level, try to handle invoices in a generic way.
 - Display ongoing payments in send tab.

electrum/util.py

@@ -73,19 +73,26 @@ base_units_list = ['BTC', 'mBTC', 'bits', 'sat']  # list(dict) does not guarante
 
 DECIMAL_POINT_DEFAULT = 5  # mBTC
 
+# types of payment requests
+PR_TYPE_ADDRESS = 0
+PR_TYPE_BIP70= 1
+PR_TYPE_LN = 2
+
 # status of payment requests
-PR_UNPAID  = 0
-PR_EXPIRED = 1
-PR_UNKNOWN = 2     # sent but not propagated
-PR_PAID    = 3     # send and propagated
-PR_INFLIGHT = 4    # unconfirmed
+PR_UNPAID   = 0
+PR_EXPIRED  = 1
+PR_UNKNOWN  = 2     # sent but not propagated
+PR_PAID     = 3     # send and propagated
+PR_INFLIGHT = 4     # unconfirmed
+PR_FAILED   = 5
 
 pr_tooltips = {
     PR_UNPAID:_('Pending'),
     PR_PAID:_('Paid'),
     PR_UNKNOWN:_('Unknown'),
     PR_EXPIRED:_('Expired'),
-    PR_INFLIGHT:_('Paid (unconfirmed)')
+    PR_INFLIGHT:_('In progress'),
+    PR_FAILED:_('Failed'),
 }
 
 pr_expiration_values = {