qml: add QR code imageprovider using qrcode/PIL

adds buildozer 'pillow' recipe to requirements

add initial PoC on qml receive tab

electrum/gui/qml/components/Receive.qml

@@ -0,0 +1,32 @@
+import QtQuick 2.6
+import QtQuick.Layouts 1.0
+import QtQuick.Controls 2.0
+import QtQuick.Controls.Material 2.0
+
+import org.electrum 1.0
+
+Pane {
+    id: rootItem
+    visible: Daemon.currentWallet !== undefined
+
+    ColumnLayout {
+        width: parent.width
+        spacing: 20
+
+        Image {
+            id: img
+        }
+
+        TextField {
+            id: text
+        }
+
+        Button {
+            text: 'generate'
+            onClicked: {
+                img.source = 'image://qrgen/' + text.text
+            }
+        }
+    }
+
+}