qml: add channel backup option to channel details page

electrum/gui/qml/components/ChannelDetails.qml

@@ -22,8 +22,17 @@ Pane {
             icon.color: 'transparent'
             action: Action {
                 text: qsTr('Backup');
-                enabled: false
+                enabled: true
-                onTriggered: {}
+                onTriggered: {
+                    var dialog = app.genericShareDialog.createObject(root,
+                        {
+                            title: qsTr('Channel Backup for %1').arg(channeldetails.short_cid),
+                            text: channeldetails.channelBackup(),
+                            text_help: channeldetails.channelBackupHelpText()
+                        }
+                    )
+                    dialog.open()
+                }
                 icon.source: '../../icons/file.png'
             }
         }

electrum/gui/qml/qechanneldetails.py

@@ -188,3 +188,15 @@ class QEChannelDetails(QObject, QtEventListener):
     @pyqtSlot()
     def deleteChannel(self):
         self._wallet.wallet.lnworker.remove_channel(self._channel.channel_id)
+
+    @pyqtSlot(result=str)
+    def channelBackup(self):
+        return self._wallet.wallet.lnworker.export_channel_backup(self._channel.channel_id)
+
+    @pyqtSlot(result=str)
+    def channelBackupHelpText(self):
+        return ' '.join([
+            _("Channel backups can be imported in another instance of the same wallet, by scanning this QR code."),
+            _("Please note that channel backups cannot be used to restore your channels."),
+            _("If you lose your wallet file, the only thing you can do with a backup is to request your channel to be closed, so that your funds will be sent on-chain."),
+        ])