qml: stop showing seconds in tx history timestamps

Reduces the precision of the date field in the qml transaction history
list to minutes. Seconds don't seem very useful in practice and add
clutter to the UI. This adapts the behaviour to the Qt GUI.

electrum/gui/qml/qetransactionlistmodel.py

@@ -162,7 +162,8 @@ class QETransactionListModel(QAbstractListModel, QtEventListener):
 
         return item
 
-    def get_section_by_timestamp(self, timestamp):
+    @staticmethod
+    def get_section_by_timestamp(timestamp):
         txts = datetime.fromtimestamp(timestamp)
         today = datetime.today().replace(hour=0, minute=0, second=0, microsecond=0)
 
@@ -177,14 +178,15 @@ class QETransactionListModel(QAbstractListModel, QtEventListener):
         else:
             return 'older'
 
-    def format_date_by_section(self, section, date):
+    @staticmethod
+    def format_date_by_section(section: str, date: datetime):
         # TODO: l10n
         dfmt = {
-            'today': '%H:%M:%S',
-            'yesterday': '%H:%M:%S',
-            'lastweek': '%a, %H:%M:%S',
-            'lastmonth': '%a %d, %H:%M:%S',
-            'older': '%Y-%m-%d %H:%M:%S'
+            'today': '%H:%M',
+            'yesterday': '%H:%M',
+            'lastweek': '%a, %H:%M',
+            'lastmonth': '%a %d, %H:%M',
+            'older': '%Y-%m-%d %H:%M'
         }
         if section not in dfmt:
             section = 'older'