add a QEAmount type for storing/passing BTC amounts in the widest sense

from a UI perspective. Stores sats, millisats (LN), whether MAX amount is
requested etc

some refactor QEInvoice type and Send page

electrum/gui/qml/components/ConfirmInvoiceDialog.qml

@@ -11,6 +11,7 @@ Dialog {
     id: dialog
 
     property Invoice invoice
+    property string invoice_key
 
     width: parent.width
     height: parent.height
@@ -84,9 +85,20 @@ Dialog {
             }
         }
 
+        Label {
+            text: qsTr('Expiration')
+            visible: true
+        }
+
+        Label {
+            id: expiration
+            text: invoice.time + invoice.expiration
+        }
+
         RowLayout {
             Layout.columnSpan: 2
-            Layout.alignment: Qt.AlignHCenter
+            Layout.alignment: Qt.AlignHCenter | Qt.AlignBottom
+            Layout.fillHeight: true
             spacing: constants.paddingMedium
 
             Button {
@@ -115,4 +127,9 @@ Dialog {
 
     }
 
+    Component.onCompleted: {
+        if (invoice_key != '') {
+            invoice.initFromKey(invoice_key)
+        }
+    }
 }

electrum/gui/qml/components/Send.qml

@@ -213,7 +213,12 @@ Pane {
                 model: DelegateModel {
                     id: delegateModel
                     model: Daemon.currentWallet.invoiceModel
-                    delegate: InvoiceDelegate {}
+                    delegate: InvoiceDelegate {
+                        onClicked: {
+                            var dialog = confirmInvoiceDialog.createObject(app, {'invoice' : invoice, 'invoice_key': model.key})
+                            dialog.open()
+                        }
+                    }
                 }
 
                 remove: Transition {
@@ -288,9 +293,7 @@ Pane {
                 // and maybe store invoice if expiry allows
             }
         }
-        onInvoiceTypeChanged: {
-            if (invoiceType == Invoice.Invalid)
-                return
+        onValidationSuccess: {
             // address only -> fill form fields
             // else -> show invoice confirmation dialog
             if (invoiceType == Invoice.OnchainOnlyAddress)